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  <div class="section" id="module-re">
<span id="re-regular-expression-operations"></span><h1>6.2. <a class="reference internal" href="#module-re" title="re: Regular expression operations."><code class="xref py py-mod docutils literal notranslate"><span class="pre">re</span></code></a> --- Regular expression operations<a class="headerlink" href="#module-re" title="永久链接至标题">¶</a></h1>
<p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.6/Lib/re.py">Lib/re.py</a></p>
<hr class="docutils" />
<p>This module provides regular expression matching operations similar to
those found in Perl.</p>
<p>Both patterns and strings to be searched can be Unicode strings (<a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a>)
as well as 8-bit strings (<a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate"><span class="pre">bytes</span></code></a>).
However, Unicode strings and 8-bit strings cannot be mixed:
that is, you cannot match a Unicode string with a byte pattern or
vice-versa; similarly, when asking for a substitution, the replacement
string must be of the same type as both the pattern and the search string.</p>
<p>Regular expressions use the backslash character (<code class="docutils literal notranslate"><span class="pre">'\'</span></code>) to indicate
special forms or to allow special characters to be used without invoking
their special meaning.  This collides with Python's usage of the same
character for the same purpose in string literals; for example, to match
a literal backslash, one might have to write <code class="docutils literal notranslate"><span class="pre">'\\\\'</span></code> as the pattern
string, because the regular expression must be <code class="docutils literal notranslate"><span class="pre">\\</span></code>, and each
backslash must be expressed as <code class="docutils literal notranslate"><span class="pre">\\</span></code> inside a regular Python string
literal.</p>
<p>The solution is to use Python's raw string notation for regular expression
patterns; backslashes are not handled in any special way in a string literal
prefixed with <code class="docutils literal notranslate"><span class="pre">'r'</span></code>.  So <code class="docutils literal notranslate"><span class="pre">r&quot;\n&quot;</span></code> is a two-character string containing
<code class="docutils literal notranslate"><span class="pre">'\'</span></code> and <code class="docutils literal notranslate"><span class="pre">'n'</span></code>, while <code class="docutils literal notranslate"><span class="pre">&quot;\n&quot;</span></code> is a one-character string containing a
newline.  Usually patterns will be expressed in Python code using this raw
string notation.</p>
<p>It is important to note that most regular expression operations are available as
module-level functions and methods on
<a class="reference internal" href="#re-objects"><span class="std std-ref">compiled regular expressions</span></a>.  The functions are shortcuts
that don't require you to compile a regex object first, but miss some
fine-tuning parameters.</p>
<div class="admonition seealso">
<p class="first admonition-title">参见</p>
<p class="last">The third-party <a class="reference external" href="https://pypi.org/project/regex/">regex</a> module,
which has an API compatible with the standard library <a class="reference internal" href="#module-re" title="re: Regular expression operations."><code class="xref py py-mod docutils literal notranslate"><span class="pre">re</span></code></a> module,
but offers additional functionality and a more thorough Unicode support.</p>
</div>
<div class="section" id="regular-expression-syntax">
<span id="re-syntax"></span><h2>6.2.1. Regular Expression Syntax<a class="headerlink" href="#regular-expression-syntax" title="永久链接至标题">¶</a></h2>
<p>A regular expression (or RE) specifies a set of strings that matches it; the
functions in this module let you check if a particular string matches a given
regular expression (or if a given regular expression matches a particular
string, which comes down to the same thing).</p>
<p>Regular expressions can be concatenated to form new regular expressions; if <em>A</em>
and <em>B</em> are both regular expressions, then <em>AB</em> is also a regular expression.
In general, if a string <em>p</em> matches <em>A</em> and another string <em>q</em> matches <em>B</em>, the
string <em>pq</em> will match AB.  This holds unless <em>A</em> or <em>B</em> contain low precedence
operations; boundary conditions between <em>A</em> and <em>B</em>; or have numbered group
references.  Thus, complex expressions can easily be constructed from simpler
primitive expressions like the ones described here.  For details of the theory
and implementation of regular expressions, consult the Friedl book <a class="reference internal" href="#frie09" id="id1">[Frie09]</a>,
or almost any textbook about compiler construction.</p>
<p>A brief explanation of the format of regular expressions follows.  For further
information and a gentler presentation, consult the <a class="reference internal" href="../howto/regex.html#regex-howto"><span class="std std-ref">Regular Expression HOWTO</span></a>.</p>
<p>Regular expressions can contain both special and ordinary characters. Most
ordinary characters, like <code class="docutils literal notranslate"><span class="pre">'A'</span></code>, <code class="docutils literal notranslate"><span class="pre">'a'</span></code>, or <code class="docutils literal notranslate"><span class="pre">'0'</span></code>, are the simplest regular
expressions; they simply match themselves.  You can concatenate ordinary
characters, so <code class="docutils literal notranslate"><span class="pre">last</span></code> matches the string <code class="docutils literal notranslate"><span class="pre">'last'</span></code>.  (In the rest of this
section, we'll write RE's in <code class="docutils literal notranslate"><span class="pre">this</span> <span class="pre">special</span> <span class="pre">style</span></code>, usually without quotes, and
strings to be matched <code class="docutils literal notranslate"><span class="pre">'in</span> <span class="pre">single</span> <span class="pre">quotes'</span></code>.)</p>
<p>Some characters, like <code class="docutils literal notranslate"><span class="pre">'|'</span></code> or <code class="docutils literal notranslate"><span class="pre">'('</span></code>, are special. Special
characters either stand for classes of ordinary characters, or affect
how the regular expressions around them are interpreted.</p>
<p>Repetition qualifiers (<code class="docutils literal notranslate"><span class="pre">*</span></code>, <code class="docutils literal notranslate"><span class="pre">+</span></code>, <code class="docutils literal notranslate"><span class="pre">?</span></code>, <code class="docutils literal notranslate"><span class="pre">{m,n}</span></code>, etc) cannot be
directly nested. This avoids ambiguity with the non-greedy modifier suffix
<code class="docutils literal notranslate"><span class="pre">?</span></code>, and with other modifiers in other implementations. To apply a second
repetition to an inner repetition, parentheses may be used. For example,
the expression <code class="docutils literal notranslate"><span class="pre">(?:a{6})*</span></code> matches any multiple of six <code class="docutils literal notranslate"><span class="pre">'a'</span></code> characters.</p>
<p>The special characters are:</p>
<dl class="docutils">
<dt><code class="docutils literal notranslate"><span class="pre">.</span></code></dt>
<dd>(Dot.)  In the default mode, this matches any character except a newline.  If
the <a class="reference internal" href="#re.DOTALL" title="re.DOTALL"><code class="xref py py-const docutils literal notranslate"><span class="pre">DOTALL</span></code></a> flag has been specified, this matches any character
including a newline.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">^</span></code></dt>
<dd>(Caret.)  Matches the start of the string, and in <a class="reference internal" href="#re.MULTILINE" title="re.MULTILINE"><code class="xref py py-const docutils literal notranslate"><span class="pre">MULTILINE</span></code></a> mode also
matches immediately after each newline.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">$</span></code></dt>
<dd>Matches the end of the string or just before the newline at the end of the
string, and in <a class="reference internal" href="#re.MULTILINE" title="re.MULTILINE"><code class="xref py py-const docutils literal notranslate"><span class="pre">MULTILINE</span></code></a> mode also matches before a newline.  <code class="docutils literal notranslate"><span class="pre">foo</span></code>
matches both 'foo' and 'foobar', while the regular expression <code class="docutils literal notranslate"><span class="pre">foo$</span></code> matches
only 'foo'.  More interestingly, searching for <code class="docutils literal notranslate"><span class="pre">foo.$</span></code> in <code class="docutils literal notranslate"><span class="pre">'foo1\nfoo2\n'</span></code>
matches 'foo2' normally, but 'foo1' in <a class="reference internal" href="#re.MULTILINE" title="re.MULTILINE"><code class="xref py py-const docutils literal notranslate"><span class="pre">MULTILINE</span></code></a> mode; searching for
a single <code class="docutils literal notranslate"><span class="pre">$</span></code> in <code class="docutils literal notranslate"><span class="pre">'foo\n'</span></code> will find two (empty) matches: one just before
the newline, and one at the end of the string.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">*</span></code></dt>
<dd>Causes the resulting RE to match 0 or more repetitions of the preceding RE, as
many repetitions as are possible.  <code class="docutils literal notranslate"><span class="pre">ab*</span></code> will match 'a', 'ab', or 'a' followed
by any number of 'b's.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">+</span></code></dt>
<dd>Causes the resulting RE to match 1 or more repetitions of the preceding RE.
<code class="docutils literal notranslate"><span class="pre">ab+</span></code> will match 'a' followed by any non-zero number of 'b's; it will not
match just 'a'.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">?</span></code></dt>
<dd>Causes the resulting RE to match 0 or 1 repetitions of the preceding RE.
<code class="docutils literal notranslate"><span class="pre">ab?</span></code> will match either 'a' or 'ab'.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">*?</span></code>, <code class="docutils literal notranslate"><span class="pre">+?</span></code>, <code class="docutils literal notranslate"><span class="pre">??</span></code></dt>
<dd>The <code class="docutils literal notranslate"><span class="pre">'*'</span></code>, <code class="docutils literal notranslate"><span class="pre">'+'</span></code>, and <code class="docutils literal notranslate"><span class="pre">'?'</span></code> qualifiers are all <em class="dfn">greedy</em>; they match
as much text as possible.  Sometimes this behaviour isn't desired; if the RE
<code class="docutils literal notranslate"><span class="pre">&lt;.*&gt;</span></code> is matched against <code class="docutils literal notranslate"><span class="pre">'&lt;a&gt;</span> <span class="pre">b</span> <span class="pre">&lt;c&gt;'</span></code>, it will match the entire
string, and not just <code class="docutils literal notranslate"><span class="pre">'&lt;a&gt;'</span></code>.  Adding <code class="docutils literal notranslate"><span class="pre">?</span></code> after the qualifier makes it
perform the match in <em class="dfn">non-greedy</em> or <em class="dfn">minimal</em> fashion; as <em>few</em>
characters as possible will be matched.  Using the RE <code class="docutils literal notranslate"><span class="pre">&lt;.*?&gt;</span></code> will match
only <code class="docutils literal notranslate"><span class="pre">'&lt;a&gt;'</span></code>.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">{m}</span></code></dt>
<dd>Specifies that exactly <em>m</em> copies of the previous RE should be matched; fewer
matches cause the entire RE not to match.  For example, <code class="docutils literal notranslate"><span class="pre">a{6}</span></code> will match
exactly six <code class="docutils literal notranslate"><span class="pre">'a'</span></code> characters, but not five.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">{m,n}</span></code></dt>
<dd>Causes the resulting RE to match from <em>m</em> to <em>n</em> repetitions of the preceding
RE, attempting to match as many repetitions as possible.  For example,
<code class="docutils literal notranslate"><span class="pre">a{3,5}</span></code> will match from 3 to 5 <code class="docutils literal notranslate"><span class="pre">'a'</span></code> characters.  Omitting <em>m</em> specifies a
lower bound of zero,  and omitting <em>n</em> specifies an infinite upper bound.  As an
example, <code class="docutils literal notranslate"><span class="pre">a{4,}b</span></code> will match <code class="docutils literal notranslate"><span class="pre">'aaaab'</span></code> or a thousand <code class="docutils literal notranslate"><span class="pre">'a'</span></code> characters
followed by a <code class="docutils literal notranslate"><span class="pre">'b'</span></code>, but not <code class="docutils literal notranslate"><span class="pre">'aaab'</span></code>. The comma may not be omitted or the
modifier would be confused with the previously described form.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">{m,n}?</span></code></dt>
<dd>Causes the resulting RE to match from <em>m</em> to <em>n</em> repetitions of the preceding
RE, attempting to match as <em>few</em> repetitions as possible.  This is the
non-greedy version of the previous qualifier.  For example, on the
6-character string <code class="docutils literal notranslate"><span class="pre">'aaaaaa'</span></code>, <code class="docutils literal notranslate"><span class="pre">a{3,5}</span></code> will match 5 <code class="docutils literal notranslate"><span class="pre">'a'</span></code> characters,
while <code class="docutils literal notranslate"><span class="pre">a{3,5}?</span></code> will only match 3 characters.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">\</span></code></dt>
<dd><p class="first">Either escapes special characters (permitting you to match characters like
<code class="docutils literal notranslate"><span class="pre">'*'</span></code>, <code class="docutils literal notranslate"><span class="pre">'?'</span></code>, and so forth), or signals a special sequence; special
sequences are discussed below.</p>
<p class="last">If you're not using a raw string to express the pattern, remember that Python
also uses the backslash as an escape sequence in string literals; if the escape
sequence isn't recognized by Python's parser, the backslash and subsequent
character are included in the resulting string.  However, if Python would
recognize the resulting sequence, the backslash should be repeated twice.  This
is complicated and hard to understand, so it's highly recommended that you use
raw strings for all but the simplest expressions.</p>
</dd>
<dt><code class="docutils literal notranslate"><span class="pre">[]</span></code></dt>
<dd><p class="first">Used to indicate a set of characters.  In a set:</p>
<ul class="last simple">
<li>Characters can be listed individually, e.g. <code class="docutils literal notranslate"><span class="pre">[amk]</span></code> will match <code class="docutils literal notranslate"><span class="pre">'a'</span></code>,
<code class="docutils literal notranslate"><span class="pre">'m'</span></code>, or <code class="docutils literal notranslate"><span class="pre">'k'</span></code>.</li>
<li>Ranges of characters can be indicated by giving two characters and separating
them by a <code class="docutils literal notranslate"><span class="pre">'-'</span></code>, for example <code class="docutils literal notranslate"><span class="pre">[a-z]</span></code> will match any lowercase ASCII letter,
<code class="docutils literal notranslate"><span class="pre">[0-5][0-9]</span></code> will match all the two-digits numbers from <code class="docutils literal notranslate"><span class="pre">00</span></code> to <code class="docutils literal notranslate"><span class="pre">59</span></code>, and
<code class="docutils literal notranslate"><span class="pre">[0-9A-Fa-f]</span></code> will match any hexadecimal digit.  If <code class="docutils literal notranslate"><span class="pre">-</span></code> is escaped (e.g.
<code class="docutils literal notranslate"><span class="pre">[a\-z]</span></code>) or if it's placed as the first or last character
(e.g. <code class="docutils literal notranslate"><span class="pre">[-a]</span></code> or <code class="docutils literal notranslate"><span class="pre">[a-]</span></code>), it will match a literal <code class="docutils literal notranslate"><span class="pre">'-'</span></code>.</li>
<li>Special characters lose their special meaning inside sets.  For example,
<code class="docutils literal notranslate"><span class="pre">[(+*)]</span></code> will match any of the literal characters <code class="docutils literal notranslate"><span class="pre">'('</span></code>, <code class="docutils literal notranslate"><span class="pre">'+'</span></code>,
<code class="docutils literal notranslate"><span class="pre">'*'</span></code>, or <code class="docutils literal notranslate"><span class="pre">')'</span></code>.</li>
<li>Character classes such as <code class="docutils literal notranslate"><span class="pre">\w</span></code> or <code class="docutils literal notranslate"><span class="pre">\S</span></code> (defined below) are also accepted
inside a set, although the characters they match depends on whether
<a class="reference internal" href="#re.ASCII" title="re.ASCII"><code class="xref py py-const docutils literal notranslate"><span class="pre">ASCII</span></code></a> or <a class="reference internal" href="#re.LOCALE" title="re.LOCALE"><code class="xref py py-const docutils literal notranslate"><span class="pre">LOCALE</span></code></a> mode is in force.</li>
<li>Characters that are not within a range can be matched by <em class="dfn">complementing</em>
the set.  If the first character of the set is <code class="docutils literal notranslate"><span class="pre">'^'</span></code>, all the characters
that are <em>not</em> in the set will be matched.  For example, <code class="docutils literal notranslate"><span class="pre">[^5]</span></code> will match
any character except <code class="docutils literal notranslate"><span class="pre">'5'</span></code>, and <code class="docutils literal notranslate"><span class="pre">[^^]</span></code> will match any character except
<code class="docutils literal notranslate"><span class="pre">'^'</span></code>.  <code class="docutils literal notranslate"><span class="pre">^</span></code> has no special meaning if it's not the first character in
the set.</li>
<li>To match a literal <code class="docutils literal notranslate"><span class="pre">']'</span></code> inside a set, precede it with a backslash, or
place it at the beginning of the set.  For example, both <code class="docutils literal notranslate"><span class="pre">[()[\]{}]</span></code> and
<code class="docutils literal notranslate"><span class="pre">[]()[{}]</span></code> will both match a parenthesis.</li>
</ul>
</dd>
<dt><code class="docutils literal notranslate"><span class="pre">|</span></code></dt>
<dd><code class="docutils literal notranslate"><span class="pre">A|B</span></code>, where <em>A</em> and <em>B</em> can be arbitrary REs, creates a regular expression that
will match either <em>A</em> or <em>B</em>.  An arbitrary number of REs can be separated by the
<code class="docutils literal notranslate"><span class="pre">'|'</span></code> in this way.  This can be used inside groups (see below) as well.  As
the target string is scanned, REs separated by <code class="docutils literal notranslate"><span class="pre">'|'</span></code> are tried from left to
right. When one pattern completely matches, that branch is accepted. This means
that once <em>A</em> matches, <em>B</em> will not be tested further, even if it would
produce a longer overall match.  In other words, the <code class="docutils literal notranslate"><span class="pre">'|'</span></code> operator is never
greedy.  To match a literal <code class="docutils literal notranslate"><span class="pre">'|'</span></code>, use <code class="docutils literal notranslate"><span class="pre">\|</span></code>, or enclose it inside a
character class, as in <code class="docutils literal notranslate"><span class="pre">[|]</span></code>.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">(...)</span></code></dt>
<dd>Matches whatever regular expression is inside the parentheses, and indicates the
start and end of a group; the contents of a group can be retrieved after a match
has been performed, and can be matched later in the string with the <code class="docutils literal notranslate"><span class="pre">\number</span></code>
special sequence, described below.  To match the literals <code class="docutils literal notranslate"><span class="pre">'('</span></code> or <code class="docutils literal notranslate"><span class="pre">')'</span></code>,
use <code class="docutils literal notranslate"><span class="pre">\(</span></code> or <code class="docutils literal notranslate"><span class="pre">\)</span></code>, or enclose them inside a character class: <code class="docutils literal notranslate"><span class="pre">[(]</span></code>, <code class="docutils literal notranslate"><span class="pre">[)]</span></code>.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">(?...)</span></code></dt>
<dd>This is an extension notation (a <code class="docutils literal notranslate"><span class="pre">'?'</span></code> following a <code class="docutils literal notranslate"><span class="pre">'('</span></code> is not meaningful
otherwise).  The first character after the <code class="docutils literal notranslate"><span class="pre">'?'</span></code> determines what the meaning
and further syntax of the construct is. Extensions usually do not create a new
group; <code class="docutils literal notranslate"><span class="pre">(?P&lt;name&gt;...)</span></code> is the only exception to this rule. Following are the
currently supported extensions.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">(?aiLmsux)</span></code></dt>
<dd>(One or more letters from the set <code class="docutils literal notranslate"><span class="pre">'a'</span></code>, <code class="docutils literal notranslate"><span class="pre">'i'</span></code>, <code class="docutils literal notranslate"><span class="pre">'L'</span></code>, <code class="docutils literal notranslate"><span class="pre">'m'</span></code>,
<code class="docutils literal notranslate"><span class="pre">'s'</span></code>, <code class="docutils literal notranslate"><span class="pre">'u'</span></code>, <code class="docutils literal notranslate"><span class="pre">'x'</span></code>.)  The group matches the empty string; the
letters set the corresponding flags: <a class="reference internal" href="#re.A" title="re.A"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.A</span></code></a> (ASCII-only matching),
<a class="reference internal" href="#re.I" title="re.I"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.I</span></code></a> (ignore case), <a class="reference internal" href="#re.L" title="re.L"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.L</span></code></a> (locale dependent),
<a class="reference internal" href="#re.M" title="re.M"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.M</span></code></a> (multi-line), <a class="reference internal" href="#re.S" title="re.S"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.S</span></code></a> (dot matches all),
<code class="xref py py-const docutils literal notranslate"><span class="pre">re.U</span></code> (Unicode matching), and <a class="reference internal" href="#re.X" title="re.X"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.X</span></code></a> (verbose),
for the entire regular expression.
(The flags are described in <a class="reference internal" href="#contents-of-module-re"><span class="std std-ref">Module Contents</span></a>.)
This is useful if you wish to include the flags as part of the
regular expression, instead of passing a <em>flag</em> argument to the
<a class="reference internal" href="#re.compile" title="re.compile"><code class="xref py py-func docutils literal notranslate"><span class="pre">re.compile()</span></code></a> function.  Flags should be used first in the
expression string.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">(?:...)</span></code></dt>
<dd>A non-capturing version of regular parentheses.  Matches whatever regular
expression is inside the parentheses, but the substring matched by the group
<em>cannot</em> be retrieved after performing a match or referenced later in the
pattern.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">(?imsx-imsx:...)</span></code></dt>
<dd><p class="first">(Zero or more letters from the set <code class="docutils literal notranslate"><span class="pre">'i'</span></code>, <code class="docutils literal notranslate"><span class="pre">'m'</span></code>, <code class="docutils literal notranslate"><span class="pre">'s'</span></code>, <code class="docutils literal notranslate"><span class="pre">'x'</span></code>,
optionally followed by <code class="docutils literal notranslate"><span class="pre">'-'</span></code> followed by one or more letters from the
same set.)  The letters set or removes the corresponding flags:
<a class="reference internal" href="#re.I" title="re.I"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.I</span></code></a> (ignore case), <a class="reference internal" href="#re.M" title="re.M"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.M</span></code></a> (multi-line), <a class="reference internal" href="#re.S" title="re.S"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.S</span></code></a>
(dot matches all), and <a class="reference internal" href="#re.X" title="re.X"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.X</span></code></a> (verbose), for the part of the
expression.  (The flags are described in <a class="reference internal" href="#contents-of-module-re"><span class="std std-ref">Module Contents</span></a>.)</p>
<div class="last versionadded">
<p><span class="versionmodified">3.6 新版功能.</span></p>
</div>
</dd>
<dt><code class="docutils literal notranslate"><span class="pre">(?P&lt;name&gt;...)</span></code></dt>
<dd><p class="first">Similar to regular parentheses, but the substring matched by the group is
accessible via the symbolic group name <em>name</em>.  Group names must be valid
Python identifiers, and each group name must be defined only once within a
regular expression.  A symbolic group is also a numbered group, just as if
the group were not named.</p>
<p>Named groups can be referenced in three contexts.  If the pattern is
<code class="docutils literal notranslate"><span class="pre">(?P&lt;quote&gt;['&quot;]).*?(?P=quote)</span></code> (i.e. matching a string quoted with either
single or double quotes):</p>
<table border="1" class="last docutils">
<colgroup>
<col width="53%" />
<col width="47%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">Context of reference to group &quot;quote&quot;</th>
<th class="head">Ways to reference it</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td>in the same pattern itself</td>
<td><ul class="first last simple">
<li><code class="docutils literal notranslate"><span class="pre">(?P=quote)</span></code> (as shown)</li>
<li><code class="docutils literal notranslate"><span class="pre">\1</span></code></li>
</ul>
</td>
</tr>
<tr class="row-odd"><td>when processing match object <em>m</em></td>
<td><ul class="first last simple">
<li><code class="docutils literal notranslate"><span class="pre">m.group('quote')</span></code></li>
<li><code class="docutils literal notranslate"><span class="pre">m.end('quote')</span></code> (etc.)</li>
</ul>
</td>
</tr>
<tr class="row-even"><td>in a string passed to the <em>repl</em>
argument of <code class="docutils literal notranslate"><span class="pre">re.sub()</span></code></td>
<td><ul class="first last simple">
<li><code class="docutils literal notranslate"><span class="pre">\g&lt;quote&gt;</span></code></li>
<li><code class="docutils literal notranslate"><span class="pre">\g&lt;1&gt;</span></code></li>
<li><code class="docutils literal notranslate"><span class="pre">\1</span></code></li>
</ul>
</td>
</tr>
</tbody>
</table>
</dd>
<dt><code class="docutils literal notranslate"><span class="pre">(?P=name)</span></code></dt>
<dd>A backreference to a named group; it matches whatever text was matched by the
earlier group named <em>name</em>.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">(?#...)</span></code></dt>
<dd>A comment; the contents of the parentheses are simply ignored.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">(?=...)</span></code></dt>
<dd>Matches if <code class="docutils literal notranslate"><span class="pre">...</span></code> matches next, but doesn't consume any of the string.  This is
called a <em class="dfn">lookahead assertion</em>.  For example, <code class="docutils literal notranslate"><span class="pre">Isaac</span> <span class="pre">(?=Asimov)</span></code> will match
<code class="docutils literal notranslate"><span class="pre">'Isaac</span> <span class="pre">'</span></code> only if it's followed by <code class="docutils literal notranslate"><span class="pre">'Asimov'</span></code>.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">(?!...)</span></code></dt>
<dd>Matches if <code class="docutils literal notranslate"><span class="pre">...</span></code> doesn't match next.  This is a <em class="dfn">negative lookahead assertion</em>.
For example, <code class="docutils literal notranslate"><span class="pre">Isaac</span> <span class="pre">(?!Asimov)</span></code> will match <code class="docutils literal notranslate"><span class="pre">'Isaac</span> <span class="pre">'</span></code> only if it's <em>not</em>
followed by <code class="docutils literal notranslate"><span class="pre">'Asimov'</span></code>.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">(?&lt;=...)</span></code></dt>
<dd><p class="first">Matches if the current position in the string is preceded by a match for <code class="docutils literal notranslate"><span class="pre">...</span></code>
that ends at the current position.  This is called a <em class="dfn">positive lookbehind
assertion</em>. <code class="docutils literal notranslate"><span class="pre">(?&lt;=abc)def</span></code> will find a match in <code class="docutils literal notranslate"><span class="pre">'abcdef'</span></code>, since the
lookbehind will back up 3 characters and check if the contained pattern matches.
The contained pattern must only match strings of some fixed length, meaning that
<code class="docutils literal notranslate"><span class="pre">abc</span></code> or <code class="docutils literal notranslate"><span class="pre">a|b</span></code> are allowed, but <code class="docutils literal notranslate"><span class="pre">a*</span></code> and <code class="docutils literal notranslate"><span class="pre">a{3,4}</span></code> are not.  Note that
patterns which start with positive lookbehind assertions will not match at the
beginning of the string being searched; you will most likely want to use the
<a class="reference internal" href="#re.search" title="re.search"><code class="xref py py-func docutils literal notranslate"><span class="pre">search()</span></code></a> function rather than the <a class="reference internal" href="#re.match" title="re.match"><code class="xref py py-func docutils literal notranslate"><span class="pre">match()</span></code></a> function:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">import</span> <span class="nn">re</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s1">&#39;(?&lt;=abc)def&#39;</span><span class="p">,</span> <span class="s1">&#39;abcdef&#39;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span>
<span class="go">&#39;def&#39;</span>
</pre></div>
</div>
<p>This example looks for a word following a hyphen:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="sa">r</span><span class="s1">&#39;(?&lt;=-)\w+&#39;</span><span class="p">,</span> <span class="s1">&#39;spam-egg&#39;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span>
<span class="go">&#39;egg&#39;</span>
</pre></div>
</div>
<div class="last versionchanged">
<p><span class="versionmodified">在 3.5 版更改: </span>Added support for group references of fixed length.</p>
</div>
</dd>
<dt><code class="docutils literal notranslate"><span class="pre">(?&lt;!...)</span></code></dt>
<dd>Matches if the current position in the string is not preceded by a match for
<code class="docutils literal notranslate"><span class="pre">...</span></code>.  This is called a <em class="dfn">negative lookbehind assertion</em>.  Similar to
positive lookbehind assertions, the contained pattern must only match strings of
some fixed length.  Patterns which start with negative lookbehind assertions may
match at the beginning of the string being searched.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">(?(id/name)yes-pattern|no-pattern)</span></code></dt>
<dd>Will try to match with <code class="docutils literal notranslate"><span class="pre">yes-pattern</span></code> if the group with given <em>id</em> or
<em>name</em> exists, and with <code class="docutils literal notranslate"><span class="pre">no-pattern</span></code> if it doesn't. <code class="docutils literal notranslate"><span class="pre">no-pattern</span></code> is
optional and can be omitted. For example,
<code class="docutils literal notranslate"><span class="pre">(&lt;)?(\w+&#64;\w+(?:\.\w+)+)(?(1)&gt;|$)</span></code> is a poor email matching pattern, which
will match with <code class="docutils literal notranslate"><span class="pre">'&lt;user&#64;host.com&gt;'</span></code> as well as <code class="docutils literal notranslate"><span class="pre">'user&#64;host.com'</span></code>, but
not with <code class="docutils literal notranslate"><span class="pre">'&lt;user&#64;host.com'</span></code> nor <code class="docutils literal notranslate"><span class="pre">'user&#64;host.com&gt;'</span></code>.</dd>
</dl>
<p>The special sequences consist of <code class="docutils literal notranslate"><span class="pre">'\'</span></code> and a character from the list below.
If the ordinary character is not an ASCII digit or an ASCII letter, then the
resulting RE will match the second character.  For example, <code class="docutils literal notranslate"><span class="pre">\$</span></code> matches the
character <code class="docutils literal notranslate"><span class="pre">'$'</span></code>.</p>
<dl class="docutils">
<dt><code class="docutils literal notranslate"><span class="pre">\number</span></code></dt>
<dd>Matches the contents of the group of the same number.  Groups are numbered
starting from 1.  For example, <code class="docutils literal notranslate"><span class="pre">(.+)</span> <span class="pre">\1</span></code> matches <code class="docutils literal notranslate"><span class="pre">'the</span> <span class="pre">the'</span></code> or <code class="docutils literal notranslate"><span class="pre">'55</span> <span class="pre">55'</span></code>,
but not <code class="docutils literal notranslate"><span class="pre">'thethe'</span></code> (note the space after the group).  This special sequence
can only be used to match one of the first 99 groups.  If the first digit of
<em>number</em> is 0, or <em>number</em> is 3 octal digits long, it will not be interpreted as
a group match, but as the character with octal value <em>number</em>. Inside the
<code class="docutils literal notranslate"><span class="pre">'['</span></code> and <code class="docutils literal notranslate"><span class="pre">']'</span></code> of a character class, all numeric escapes are treated as
characters.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">\A</span></code></dt>
<dd>Matches only at the start of the string.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">\b</span></code></dt>
<dd><p class="first">Matches the empty string, but only at the beginning or end of a word.
A word is defined as a sequence of word characters.  Note that formally,
<code class="docutils literal notranslate"><span class="pre">\b</span></code> is defined as the boundary between a <code class="docutils literal notranslate"><span class="pre">\w</span></code> and a <code class="docutils literal notranslate"><span class="pre">\W</span></code> character
(or vice versa), or between <code class="docutils literal notranslate"><span class="pre">\w</span></code> and the beginning/end of the string.
This means that <code class="docutils literal notranslate"><span class="pre">r'\bfoo\b'</span></code> matches <code class="docutils literal notranslate"><span class="pre">'foo'</span></code>, <code class="docutils literal notranslate"><span class="pre">'foo.'</span></code>, <code class="docutils literal notranslate"><span class="pre">'(foo)'</span></code>,
<code class="docutils literal notranslate"><span class="pre">'bar</span> <span class="pre">foo</span> <span class="pre">baz'</span></code> but not <code class="docutils literal notranslate"><span class="pre">'foobar'</span></code> or <code class="docutils literal notranslate"><span class="pre">'foo3'</span></code>.</p>
<p class="last">By default Unicode alphanumerics are the ones used in Unicode patterns, but
this can be changed by using the <a class="reference internal" href="#re.ASCII" title="re.ASCII"><code class="xref py py-const docutils literal notranslate"><span class="pre">ASCII</span></code></a> flag.  Word boundaries are
determined by the current locale if the <a class="reference internal" href="#re.LOCALE" title="re.LOCALE"><code class="xref py py-const docutils literal notranslate"><span class="pre">LOCALE</span></code></a> flag is used.
Inside a character range, <code class="docutils literal notranslate"><span class="pre">\b</span></code> represents the backspace character, for
compatibility with Python's string literals.</p>
</dd>
<dt><code class="docutils literal notranslate"><span class="pre">\B</span></code></dt>
<dd>Matches the empty string, but only when it is <em>not</em> at the beginning or end
of a word.  This means that <code class="docutils literal notranslate"><span class="pre">r'py\B'</span></code> matches <code class="docutils literal notranslate"><span class="pre">'python'</span></code>, <code class="docutils literal notranslate"><span class="pre">'py3'</span></code>,
<code class="docutils literal notranslate"><span class="pre">'py2'</span></code>, but not <code class="docutils literal notranslate"><span class="pre">'py'</span></code>, <code class="docutils literal notranslate"><span class="pre">'py.'</span></code>, or <code class="docutils literal notranslate"><span class="pre">'py!'</span></code>.
<code class="docutils literal notranslate"><span class="pre">\B</span></code> is just the opposite of <code class="docutils literal notranslate"><span class="pre">\b</span></code>, so word characters in Unicode
patterns are Unicode alphanumerics or the underscore, although this can
be changed by using the <a class="reference internal" href="#re.ASCII" title="re.ASCII"><code class="xref py py-const docutils literal notranslate"><span class="pre">ASCII</span></code></a> flag.  Word boundaries are
determined by the current locale if the <a class="reference internal" href="#re.LOCALE" title="re.LOCALE"><code class="xref py py-const docutils literal notranslate"><span class="pre">LOCALE</span></code></a> flag is used.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">\d</span></code></dt>
<dd><dl class="first last docutils">
<dt>For Unicode (str) patterns:</dt>
<dd>Matches any Unicode decimal digit (that is, any character in
Unicode character category [Nd]).  This includes <code class="docutils literal notranslate"><span class="pre">[0-9]</span></code>, and
also many other digit characters.  If the <a class="reference internal" href="#re.ASCII" title="re.ASCII"><code class="xref py py-const docutils literal notranslate"><span class="pre">ASCII</span></code></a> flag is
used only <code class="docutils literal notranslate"><span class="pre">[0-9]</span></code> is matched (but the flag affects the entire
regular expression, so in such cases using an explicit <code class="docutils literal notranslate"><span class="pre">[0-9]</span></code>
may be a better choice).</dd>
<dt>For 8-bit (bytes) patterns:</dt>
<dd>Matches any decimal digit; this is equivalent to <code class="docutils literal notranslate"><span class="pre">[0-9]</span></code>.</dd>
</dl>
</dd>
<dt><code class="docutils literal notranslate"><span class="pre">\D</span></code></dt>
<dd>Matches any character which is not a decimal digit. This is
the opposite of <code class="docutils literal notranslate"><span class="pre">\d</span></code>. If the <a class="reference internal" href="#re.ASCII" title="re.ASCII"><code class="xref py py-const docutils literal notranslate"><span class="pre">ASCII</span></code></a> flag is used this
becomes the equivalent of <code class="docutils literal notranslate"><span class="pre">[^0-9]</span></code> (but the flag affects the entire
regular expression, so in such cases using an explicit <code class="docutils literal notranslate"><span class="pre">[^0-9]</span></code> may
be a better choice).</dd>
<dt><code class="docutils literal notranslate"><span class="pre">\s</span></code></dt>
<dd><dl class="first last docutils">
<dt>For Unicode (str) patterns:</dt>
<dd>Matches Unicode whitespace characters (which includes
<code class="docutils literal notranslate"><span class="pre">[</span> <span class="pre">\t\n\r\f\v]</span></code>, and also many other characters, for example the
non-breaking spaces mandated by typography rules in many
languages). If the <a class="reference internal" href="#re.ASCII" title="re.ASCII"><code class="xref py py-const docutils literal notranslate"><span class="pre">ASCII</span></code></a> flag is used, only
<code class="docutils literal notranslate"><span class="pre">[</span> <span class="pre">\t\n\r\f\v]</span></code> is matched (but the flag affects the entire
regular expression, so in such cases using an explicit
<code class="docutils literal notranslate"><span class="pre">[</span> <span class="pre">\t\n\r\f\v]</span></code> may be a better choice).</dd>
<dt>For 8-bit (bytes) patterns:</dt>
<dd>Matches characters considered whitespace in the ASCII character set;
this is equivalent to <code class="docutils literal notranslate"><span class="pre">[</span> <span class="pre">\t\n\r\f\v]</span></code>.</dd>
</dl>
</dd>
<dt><code class="docutils literal notranslate"><span class="pre">\S</span></code></dt>
<dd>Matches any character which is not a whitespace character. This is
the opposite of <code class="docutils literal notranslate"><span class="pre">\s</span></code>. If the <a class="reference internal" href="#re.ASCII" title="re.ASCII"><code class="xref py py-const docutils literal notranslate"><span class="pre">ASCII</span></code></a> flag is used this
becomes the equivalent of <code class="docutils literal notranslate"><span class="pre">[^</span> <span class="pre">\t\n\r\f\v]</span></code> (but the flag affects the entire
regular expression, so in such cases using an explicit <code class="docutils literal notranslate"><span class="pre">[^</span> <span class="pre">\t\n\r\f\v]</span></code> may
be a better choice).</dd>
<dt><code class="docutils literal notranslate"><span class="pre">\w</span></code></dt>
<dd><dl class="first last docutils">
<dt>For Unicode (str) patterns:</dt>
<dd>Matches Unicode word characters; this includes most characters
that can be part of a word in any language, as well as numbers and
the underscore. If the <a class="reference internal" href="#re.ASCII" title="re.ASCII"><code class="xref py py-const docutils literal notranslate"><span class="pre">ASCII</span></code></a> flag is used, only
<code class="docutils literal notranslate"><span class="pre">[a-zA-Z0-9_]</span></code> is matched (but the flag affects the entire
regular expression, so in such cases using an explicit
<code class="docutils literal notranslate"><span class="pre">[a-zA-Z0-9_]</span></code> may be a better choice).</dd>
<dt>For 8-bit (bytes) patterns:</dt>
<dd>Matches characters considered alphanumeric in the ASCII character set;
this is equivalent to <code class="docutils literal notranslate"><span class="pre">[a-zA-Z0-9_]</span></code>.  If the <a class="reference internal" href="#re.LOCALE" title="re.LOCALE"><code class="xref py py-const docutils literal notranslate"><span class="pre">LOCALE</span></code></a> flag is
used, matches characters considered alphanumeric in the current locale
and the underscore.</dd>
</dl>
</dd>
<dt><code class="docutils literal notranslate"><span class="pre">\W</span></code></dt>
<dd>Matches any character which is not a word character. This is
the opposite of <code class="docutils literal notranslate"><span class="pre">\w</span></code>. If the <a class="reference internal" href="#re.ASCII" title="re.ASCII"><code class="xref py py-const docutils literal notranslate"><span class="pre">ASCII</span></code></a> flag is used this
becomes the equivalent of <code class="docutils literal notranslate"><span class="pre">[^a-zA-Z0-9_]</span></code> (but the flag affects the
entire regular expression, so in such cases using an explicit
<code class="docutils literal notranslate"><span class="pre">[^a-zA-Z0-9_]</span></code> may be a better choice).  If the <a class="reference internal" href="#re.LOCALE" title="re.LOCALE"><code class="xref py py-const docutils literal notranslate"><span class="pre">LOCALE</span></code></a> flag is
used, matches characters considered alphanumeric in the current locale
and the underscore.</dd>
<dt><code class="docutils literal notranslate"><span class="pre">\Z</span></code></dt>
<dd>Matches only at the end of the string.</dd>
</dl>
<p>Most of the standard escapes supported by Python string literals are also
accepted by the regular expression parser:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span>\<span class="n">a</span>      \<span class="n">b</span>      \<span class="n">f</span>      \<span class="n">n</span>
\<span class="n">r</span>      \<span class="n">t</span>      \<span class="n">u</span>      \<span class="n">U</span>
\<span class="n">v</span>      \<span class="n">x</span>      \\
</pre></div>
</div>
<p>(Note that <code class="docutils literal notranslate"><span class="pre">\b</span></code> is used to represent word boundaries, and means &quot;backspace&quot;
only inside character classes.)</p>
<p><code class="docutils literal notranslate"><span class="pre">'\u'</span></code> and <code class="docutils literal notranslate"><span class="pre">'\U'</span></code> escape sequences are only recognized in Unicode
patterns.  In bytes patterns they are errors.</p>
<p>Octal escapes are included in a limited form.  If the first digit is a 0, or if
there are three octal digits, it is considered an octal escape. Otherwise, it is
a group reference.  As for string literals, octal escapes are always at most
three digits in length.</p>
<div class="versionchanged">
<p><span class="versionmodified">在 3.3 版更改: </span>The <code class="docutils literal notranslate"><span class="pre">'\u'</span></code> and <code class="docutils literal notranslate"><span class="pre">'\U'</span></code> escape sequences have been added.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">在 3.6 版更改: </span>Unknown escapes consisting of <code class="docutils literal notranslate"><span class="pre">'\'</span></code> and an ASCII letter now are errors.</p>
</div>
</div>
<div class="section" id="module-contents">
<span id="contents-of-module-re"></span><h2>6.2.2. Module Contents<a class="headerlink" href="#module-contents" title="永久链接至标题">¶</a></h2>
<p>The module defines several functions, constants, and an exception. Some of the
functions are simplified versions of the full featured methods for compiled
regular expressions.  Most non-trivial applications always use the compiled
form.</p>
<div class="versionchanged">
<p><span class="versionmodified">在 3.6 版更改: </span>Flag constants are now instances of <code class="xref py py-class docutils literal notranslate"><span class="pre">RegexFlag</span></code>, which is a subclass of
<a class="reference internal" href="enum.html#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate"><span class="pre">enum.IntFlag</span></code></a>.</p>
</div>
<dl class="function">
<dt id="re.compile">
<code class="descclassname">re.</code><code class="descname">compile</code><span class="sig-paren">(</span><em>pattern</em>, <em>flags=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.compile" title="永久链接至目标">¶</a></dt>
<dd><p>Compile a regular expression pattern into a <a class="reference internal" href="#re-objects"><span class="std std-ref">regular expression object</span></a>, which can be used for matching using its
<a class="reference internal" href="#re.regex.match" title="re.regex.match"><code class="xref py py-func docutils literal notranslate"><span class="pre">match()</span></code></a>, <a class="reference internal" href="#re.regex.search" title="re.regex.search"><code class="xref py py-func docutils literal notranslate"><span class="pre">search()</span></code></a> and other methods, described
below.</p>
<p>The expression's behaviour can be modified by specifying a <em>flags</em> value.
Values can be any of the following variables, combined using bitwise OR (the
<code class="docutils literal notranslate"><span class="pre">|</span></code> operator).</p>
<p>The sequence</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">prog</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="n">pattern</span><span class="p">)</span>
<span class="n">result</span> <span class="o">=</span> <span class="n">prog</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="n">string</span><span class="p">)</span>
</pre></div>
</div>
<p>is equivalent to</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">result</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="n">pattern</span><span class="p">,</span> <span class="n">string</span><span class="p">)</span>
</pre></div>
</div>
<p>but using <a class="reference internal" href="#re.compile" title="re.compile"><code class="xref py py-func docutils literal notranslate"><span class="pre">re.compile()</span></code></a> and saving the resulting regular expression
object for reuse is more efficient when the expression will be used several
times in a single program.</p>
<div class="admonition note">
<p class="first admonition-title">注解</p>
<p class="last">The compiled versions of the most recent patterns passed to
<a class="reference internal" href="#re.compile" title="re.compile"><code class="xref py py-func docutils literal notranslate"><span class="pre">re.compile()</span></code></a> and the module-level matching functions are cached, so
programs that use only a few regular expressions at a time needn't worry
about compiling regular expressions.</p>
</div>
</dd></dl>

<dl class="data">
<dt id="re.A">
<code class="descclassname">re.</code><code class="descname">A</code><a class="headerlink" href="#re.A" title="永久链接至目标">¶</a></dt>
<dt id="re.ASCII">
<code class="descclassname">re.</code><code class="descname">ASCII</code><a class="headerlink" href="#re.ASCII" title="永久链接至目标">¶</a></dt>
<dd><p>Make <code class="docutils literal notranslate"><span class="pre">\w</span></code>, <code class="docutils literal notranslate"><span class="pre">\W</span></code>, <code class="docutils literal notranslate"><span class="pre">\b</span></code>, <code class="docutils literal notranslate"><span class="pre">\B</span></code>, <code class="docutils literal notranslate"><span class="pre">\d</span></code>, <code class="docutils literal notranslate"><span class="pre">\D</span></code>, <code class="docutils literal notranslate"><span class="pre">\s</span></code> and <code class="docutils literal notranslate"><span class="pre">\S</span></code>
perform ASCII-only matching instead of full Unicode matching.  This is only
meaningful for Unicode patterns, and is ignored for byte patterns.
Corresponds to the inline flag <code class="docutils literal notranslate"><span class="pre">(?a)</span></code>.</p>
<p>Note that for backward compatibility, the <code class="xref py py-const docutils literal notranslate"><span class="pre">re.U</span></code> flag still
exists (as well as its synonym <code class="xref py py-const docutils literal notranslate"><span class="pre">re.UNICODE</span></code> and its embedded
counterpart <code class="docutils literal notranslate"><span class="pre">(?u)</span></code>), but these are redundant in Python 3 since
matches are Unicode by default for strings (and Unicode matching
isn't allowed for bytes).</p>
</dd></dl>

<dl class="data">
<dt id="re.DEBUG">
<code class="descclassname">re.</code><code class="descname">DEBUG</code><a class="headerlink" href="#re.DEBUG" title="永久链接至目标">¶</a></dt>
<dd><p>Display debug information about compiled expression.
No corresponding inline flag.</p>
</dd></dl>

<dl class="data">
<dt id="re.I">
<code class="descclassname">re.</code><code class="descname">I</code><a class="headerlink" href="#re.I" title="永久链接至目标">¶</a></dt>
<dt id="re.IGNORECASE">
<code class="descclassname">re.</code><code class="descname">IGNORECASE</code><a class="headerlink" href="#re.IGNORECASE" title="永久链接至目标">¶</a></dt>
<dd><p>Perform case-insensitive matching; expressions like <code class="docutils literal notranslate"><span class="pre">[A-Z]</span></code> will also
match lowercase letters.  Full Unicode matching (such as <code class="docutils literal notranslate"><span class="pre">Ü</span></code> matching
<code class="docutils literal notranslate"><span class="pre">ü</span></code>) also works unless the <a class="reference internal" href="#re.ASCII" title="re.ASCII"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.ASCII</span></code></a> flag is used to disable
non-ASCII matches.  The current locale does not change the effect of this
flag unless the <a class="reference internal" href="#re.LOCALE" title="re.LOCALE"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.LOCALE</span></code></a> flag is also used.
Corresponds to the inline flag <code class="docutils literal notranslate"><span class="pre">(?i)</span></code>.</p>
<p>Note that when the Unicode patterns <code class="docutils literal notranslate"><span class="pre">[a-z]</span></code> or <code class="docutils literal notranslate"><span class="pre">[A-Z]</span></code> are used in
combination with the <a class="reference internal" href="#re.IGNORECASE" title="re.IGNORECASE"><code class="xref py py-const docutils literal notranslate"><span class="pre">IGNORECASE</span></code></a> flag, they will match the 52 ASCII
letters and 4 additional non-ASCII letters: 'İ' (U+0130, Latin capital
letter I with dot above), 'ı' (U+0131, Latin small letter dotless i),
'ſ' (U+017F, Latin small letter long s) and 'K' (U+212A, Kelvin sign).
If the <a class="reference internal" href="#re.ASCII" title="re.ASCII"><code class="xref py py-const docutils literal notranslate"><span class="pre">ASCII</span></code></a> flag is used, only letters 'a' to 'z'
and 'A' to 'Z' are matched (but the flag affects the entire regular
expression, so in such cases using an explicit <code class="docutils literal notranslate"><span class="pre">(?-i:[a-zA-Z])</span></code> may be
a better choice).</p>
</dd></dl>

<dl class="data">
<dt id="re.L">
<code class="descclassname">re.</code><code class="descname">L</code><a class="headerlink" href="#re.L" title="永久链接至目标">¶</a></dt>
<dt id="re.LOCALE">
<code class="descclassname">re.</code><code class="descname">LOCALE</code><a class="headerlink" href="#re.LOCALE" title="永久链接至目标">¶</a></dt>
<dd><p>Make <code class="docutils literal notranslate"><span class="pre">\w</span></code>, <code class="docutils literal notranslate"><span class="pre">\W</span></code>, <code class="docutils literal notranslate"><span class="pre">\b</span></code>, <code class="docutils literal notranslate"><span class="pre">\B</span></code> and case-insensitive matching
dependent on the current locale.  This flag can be used only with bytes
patterns.  The use of this flag is discouraged as the locale mechanism
is very unreliable, it only handles one &quot;culture&quot; at a time, and it only
works with 8-bit locales.  Unicode matching is already enabled by default
in Python 3 for Unicode (str) patterns, and it is able to handle different
locales/languages.
Corresponds to the inline flag <code class="docutils literal notranslate"><span class="pre">(?L)</span></code>.</p>
<div class="versionchanged">
<p><span class="versionmodified">在 3.6 版更改: </span><a class="reference internal" href="#re.LOCALE" title="re.LOCALE"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.LOCALE</span></code></a> can be used only with bytes patterns and is
not compatible with <a class="reference internal" href="#re.ASCII" title="re.ASCII"><code class="xref py py-const docutils literal notranslate"><span class="pre">re.ASCII</span></code></a>.</p>
</div>
</dd></dl>

<dl class="data">
<dt id="re.M">
<code class="descclassname">re.</code><code class="descname">M</code><a class="headerlink" href="#re.M" title="永久链接至目标">¶</a></dt>
<dt id="re.MULTILINE">
<code class="descclassname">re.</code><code class="descname">MULTILINE</code><a class="headerlink" href="#re.MULTILINE" title="永久链接至目标">¶</a></dt>
<dd><p>When specified, the pattern character <code class="docutils literal notranslate"><span class="pre">'^'</span></code> matches at the beginning of the
string and at the beginning of each line (immediately following each newline);
and the pattern character <code class="docutils literal notranslate"><span class="pre">'$'</span></code> matches at the end of the string and at the
end of each line (immediately preceding each newline).  By default, <code class="docutils literal notranslate"><span class="pre">'^'</span></code>
matches only at the beginning of the string, and <code class="docutils literal notranslate"><span class="pre">'$'</span></code> only at the end of the
string and immediately before the newline (if any) at the end of the string.
Corresponds to the inline flag <code class="docutils literal notranslate"><span class="pre">(?m)</span></code>.</p>
</dd></dl>

<dl class="data">
<dt id="re.S">
<code class="descclassname">re.</code><code class="descname">S</code><a class="headerlink" href="#re.S" title="永久链接至目标">¶</a></dt>
<dt id="re.DOTALL">
<code class="descclassname">re.</code><code class="descname">DOTALL</code><a class="headerlink" href="#re.DOTALL" title="永久链接至目标">¶</a></dt>
<dd><p>Make the <code class="docutils literal notranslate"><span class="pre">'.'</span></code> special character match any character at all, including a
newline; without this flag, <code class="docutils literal notranslate"><span class="pre">'.'</span></code> will match anything <em>except</em> a newline.
Corresponds to the inline flag <code class="docutils literal notranslate"><span class="pre">(?s)</span></code>.</p>
</dd></dl>

<dl class="data">
<dt id="re.X">
<code class="descclassname">re.</code><code class="descname">X</code><a class="headerlink" href="#re.X" title="永久链接至目标">¶</a></dt>
<dt id="re.VERBOSE">
<code class="descclassname">re.</code><code class="descname">VERBOSE</code><a class="headerlink" href="#re.VERBOSE" title="永久链接至目标">¶</a></dt>
<dd><p>This flag allows you to write regular expressions that look nicer and are
more readable by allowing you to visually separate logical sections of the
pattern and add comments. Whitespace within the pattern is ignored, except
when in a character class, or when preceded by an unescaped backslash,
or within tokens like <code class="docutils literal notranslate"><span class="pre">*?</span></code>, <code class="docutils literal notranslate"><span class="pre">(?:</span></code> or <code class="docutils literal notranslate"><span class="pre">(?P&lt;...&gt;</span></code>.
When a line contains a <code class="docutils literal notranslate"><span class="pre">#</span></code> that is not in a character class and is not
preceded by an unescaped backslash, all characters from the leftmost such
<code class="docutils literal notranslate"><span class="pre">#</span></code> through the end of the line are ignored.</p>
<p>This means that the two following regular expression objects that match a
decimal number are functionally equal:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">a</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="sa">r</span><span class="s2">&quot;&quot;&quot;\d +  # the integral part</span>
<span class="s2">                   \.    # the decimal point</span>
<span class="s2">                   \d *  # some fractional digits&quot;&quot;&quot;</span><span class="p">,</span> <span class="n">re</span><span class="o">.</span><span class="n">X</span><span class="p">)</span>
<span class="n">b</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="sa">r</span><span class="s2">&quot;\d+\.\d*&quot;</span><span class="p">)</span>
</pre></div>
</div>
<p>Corresponds to the inline flag <code class="docutils literal notranslate"><span class="pre">(?x)</span></code>.</p>
</dd></dl>

<dl class="function">
<dt id="re.search">
<code class="descclassname">re.</code><code class="descname">search</code><span class="sig-paren">(</span><em>pattern</em>, <em>string</em>, <em>flags=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.search" title="永久链接至目标">¶</a></dt>
<dd><p>Scan through <em>string</em> looking for the first location where the regular expression
<em>pattern</em> produces a match, and return a corresponding <a class="reference internal" href="#match-objects"><span class="std std-ref">match object</span></a>.  Return <code class="docutils literal notranslate"><span class="pre">None</span></code> if no position in the string matches the
pattern; note that this is different from finding a zero-length match at some
point in the string.</p>
</dd></dl>

<dl class="function">
<dt id="re.match">
<code class="descclassname">re.</code><code class="descname">match</code><span class="sig-paren">(</span><em>pattern</em>, <em>string</em>, <em>flags=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.match" title="永久链接至目标">¶</a></dt>
<dd><p>If zero or more characters at the beginning of <em>string</em> match the regular
expression <em>pattern</em>, return a corresponding <a class="reference internal" href="#match-objects"><span class="std std-ref">match object</span></a>.  Return <code class="docutils literal notranslate"><span class="pre">None</span></code> if the string does not match the pattern;
note that this is different from a zero-length match.</p>
<p>Note that even in <a class="reference internal" href="#re.MULTILINE" title="re.MULTILINE"><code class="xref py py-const docutils literal notranslate"><span class="pre">MULTILINE</span></code></a> mode, <a class="reference internal" href="#re.match" title="re.match"><code class="xref py py-func docutils literal notranslate"><span class="pre">re.match()</span></code></a> will only match
at the beginning of the string and not at the beginning of each line.</p>
<p>If you want to locate a match anywhere in <em>string</em>, use <a class="reference internal" href="#re.search" title="re.search"><code class="xref py py-func docutils literal notranslate"><span class="pre">search()</span></code></a>
instead (see also <a class="reference internal" href="#search-vs-match"><span class="std std-ref">search() vs. match()</span></a>).</p>
</dd></dl>

<dl class="function">
<dt id="re.fullmatch">
<code class="descclassname">re.</code><code class="descname">fullmatch</code><span class="sig-paren">(</span><em>pattern</em>, <em>string</em>, <em>flags=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.fullmatch" title="永久链接至目标">¶</a></dt>
<dd><p>If the whole <em>string</em> matches the regular expression <em>pattern</em>, return a
corresponding <a class="reference internal" href="#match-objects"><span class="std std-ref">match object</span></a>.  Return <code class="docutils literal notranslate"><span class="pre">None</span></code> if the
string does not match the pattern; note that this is different from a
zero-length match.</p>
<div class="versionadded">
<p><span class="versionmodified">3.4 新版功能.</span></p>
</div>
</dd></dl>

<dl class="function">
<dt id="re.split">
<code class="descclassname">re.</code><code class="descname">split</code><span class="sig-paren">(</span><em>pattern</em>, <em>string</em>, <em>maxsplit=0</em>, <em>flags=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.split" title="永久链接至目标">¶</a></dt>
<dd><p>Split <em>string</em> by the occurrences of <em>pattern</em>.  If capturing parentheses are
used in <em>pattern</em>, then the text of all groups in the pattern are also returned
as part of the resulting list. If <em>maxsplit</em> is nonzero, at most <em>maxsplit</em>
splits occur, and the remainder of the string is returned as the final element
of the list.</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="sa">r</span><span class="s1">&#39;\W+&#39;</span><span class="p">,</span> <span class="s1">&#39;Words, words, words.&#39;</span><span class="p">)</span>
<span class="go">[&#39;Words&#39;, &#39;words&#39;, &#39;words&#39;, &#39;&#39;]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="sa">r</span><span class="s1">&#39;(\W+)&#39;</span><span class="p">,</span> <span class="s1">&#39;Words, words, words.&#39;</span><span class="p">)</span>
<span class="go">[&#39;Words&#39;, &#39;, &#39;, &#39;words&#39;, &#39;, &#39;, &#39;words&#39;, &#39;.&#39;, &#39;&#39;]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="sa">r</span><span class="s1">&#39;\W+&#39;</span><span class="p">,</span> <span class="s1">&#39;Words, words, words.&#39;</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span>
<span class="go">[&#39;Words&#39;, &#39;words, words.&#39;]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="s1">&#39;[a-f]+&#39;</span><span class="p">,</span> <span class="s1">&#39;0a3B9&#39;</span><span class="p">,</span> <span class="n">flags</span><span class="o">=</span><span class="n">re</span><span class="o">.</span><span class="n">IGNORECASE</span><span class="p">)</span>
<span class="go">[&#39;0&#39;, &#39;3&#39;, &#39;9&#39;]</span>
</pre></div>
</div>
<p>If there are capturing groups in the separator and it matches at the start of
the string, the result will start with an empty string.  The same holds for
the end of the string:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="sa">r</span><span class="s1">&#39;(\W+)&#39;</span><span class="p">,</span> <span class="s1">&#39;...words, words...&#39;</span><span class="p">)</span>
<span class="go">[&#39;&#39;, &#39;...&#39;, &#39;words&#39;, &#39;, &#39;, &#39;words&#39;, &#39;...&#39;, &#39;&#39;]</span>
</pre></div>
</div>
<p>That way, separator components are always found at the same relative
indices within the result list.</p>
<div class="admonition note">
<p class="first admonition-title">注解</p>
<p><a class="reference internal" href="#re.split" title="re.split"><code class="xref py py-func docutils literal notranslate"><span class="pre">split()</span></code></a> doesn't currently split a string on an empty pattern match.
For example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="s1">&#39;x*&#39;</span><span class="p">,</span> <span class="s1">&#39;axbc&#39;</span><span class="p">)</span>
<span class="go">[&#39;a&#39;, &#39;bc&#39;]</span>
</pre></div>
</div>
<p>Even though <code class="docutils literal notranslate"><span class="pre">'x*'</span></code> also matches 0 'x' before 'a', between 'b' and 'c',
and after 'c', currently these matches are ignored.  The correct behavior
(i.e. splitting on empty matches too and returning <code class="docutils literal notranslate"><span class="pre">['',</span> <span class="pre">'a',</span> <span class="pre">'b',</span> <span class="pre">'c',</span>
<span class="pre">'']</span></code>) will be implemented in future versions of Python, but since this
is a backward incompatible change, a <a class="reference internal" href="exceptions.html#FutureWarning" title="FutureWarning"><code class="xref py py-exc docutils literal notranslate"><span class="pre">FutureWarning</span></code></a> will be raised
in the meanwhile.</p>
<p>Patterns that can only match empty strings currently never split the
string.  Since this doesn't match the expected behavior, a
<a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> will be raised starting from Python 3.5:</p>
<div class="last highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="s2">&quot;^$&quot;</span><span class="p">,</span> <span class="s2">&quot;foo</span><span class="se">\n\n</span><span class="s2">bar</span><span class="se">\n</span><span class="s2">&quot;</span><span class="p">,</span> <span class="n">flags</span><span class="o">=</span><span class="n">re</span><span class="o">.</span><span class="n">M</span><span class="p">)</span>
<span class="gt">Traceback (most recent call last):</span>
  File <span class="nb">&quot;&lt;stdin&gt;&quot;</span>, line <span class="m">1</span>, in <span class="n">&lt;module&gt;</span>
  <span class="c">...</span>
<span class="gr">ValueError</span>: <span class="n">split() requires a non-empty pattern match.</span>
</pre></div>
</div>
</div>
<div class="versionchanged">
<p><span class="versionmodified">在 3.1 版更改: </span>Added the optional flags argument.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">在 3.5 版更改: </span>Splitting on a pattern that could match an empty string now raises
a warning.  Patterns that can only match empty strings are now rejected.</p>
</div>
</dd></dl>

<dl class="function">
<dt id="re.findall">
<code class="descclassname">re.</code><code class="descname">findall</code><span class="sig-paren">(</span><em>pattern</em>, <em>string</em>, <em>flags=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.findall" title="永久链接至目标">¶</a></dt>
<dd><p>Return all non-overlapping matches of <em>pattern</em> in <em>string</em>, as a list of
strings.  The <em>string</em> is scanned left-to-right, and matches are returned in
the order found.  If one or more groups are present in the pattern, return a
list of groups; this will be a list of tuples if the pattern has more than
one group.  Empty matches are included in the result.</p>
<div class="admonition note">
<p class="first admonition-title">注解</p>
<p class="last">Due to the limitation of the current implementation the character
following an empty match is not included in a next match, so
<code class="docutils literal notranslate"><span class="pre">findall(r'^|\w+',</span> <span class="pre">'two</span> <span class="pre">words')</span></code> returns <code class="docutils literal notranslate"><span class="pre">['',</span> <span class="pre">'wo',</span> <span class="pre">'words']</span></code>
(note missed &quot;t&quot;).  This is changed in Python 3.7.</p>
</div>
</dd></dl>

<dl class="function">
<dt id="re.finditer">
<code class="descclassname">re.</code><code class="descname">finditer</code><span class="sig-paren">(</span><em>pattern</em>, <em>string</em>, <em>flags=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.finditer" title="永久链接至目标">¶</a></dt>
<dd><p>Return an <a class="reference internal" href="../glossary.html#term-iterator"><span class="xref std std-term">iterator</span></a> yielding <a class="reference internal" href="#match-objects"><span class="std std-ref">match objects</span></a> over
all non-overlapping matches for the RE <em>pattern</em> in <em>string</em>.  The <em>string</em>
is scanned left-to-right, and matches are returned in the order found.  Empty
matches are included in the result.  See also the note about <a class="reference internal" href="#re.findall" title="re.findall"><code class="xref py py-func docutils literal notranslate"><span class="pre">findall()</span></code></a>.</p>
</dd></dl>

<dl class="function">
<dt id="re.sub">
<code class="descclassname">re.</code><code class="descname">sub</code><span class="sig-paren">(</span><em>pattern</em>, <em>repl</em>, <em>string</em>, <em>count=0</em>, <em>flags=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.sub" title="永久链接至目标">¶</a></dt>
<dd><p>Return the string obtained by replacing the leftmost non-overlapping occurrences
of <em>pattern</em> in <em>string</em> by the replacement <em>repl</em>.  If the pattern isn't found,
<em>string</em> is returned unchanged.  <em>repl</em> can be a string or a function; if it is
a string, any backslash escapes in it are processed.  That is, <code class="docutils literal notranslate"><span class="pre">\n</span></code> is
converted to a single newline character, <code class="docutils literal notranslate"><span class="pre">\r</span></code> is converted to a carriage return, and
so forth.  Unknown escapes such as <code class="docutils literal notranslate"><span class="pre">\&amp;</span></code> are left alone.  Backreferences, such
as <code class="docutils literal notranslate"><span class="pre">\6</span></code>, are replaced with the substring matched by group 6 in the pattern.
For example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">re</span><span class="o">.</span><span class="n">sub</span><span class="p">(</span><span class="sa">r</span><span class="s1">&#39;def\s+([a-zA-Z_][a-zA-Z_0-9]*)\s*\(\s*\):&#39;</span><span class="p">,</span>
<span class="gp">... </span>       <span class="sa">r</span><span class="s1">&#39;static PyObject*\npy_\1(void)\n{&#39;</span><span class="p">,</span>
<span class="gp">... </span>       <span class="s1">&#39;def myfunc():&#39;</span><span class="p">)</span>
<span class="go">&#39;static PyObject*\npy_myfunc(void)\n{&#39;</span>
</pre></div>
</div>
<p>If <em>repl</em> is a function, it is called for every non-overlapping occurrence of
<em>pattern</em>.  The function takes a single <a class="reference internal" href="#match-objects"><span class="std std-ref">match object</span></a>
argument, and returns the replacement string.  For example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">def</span> <span class="nf">dashrepl</span><span class="p">(</span><span class="n">matchobj</span><span class="p">):</span>
<span class="gp">... </span>    <span class="k">if</span> <span class="n">matchobj</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span> <span class="o">==</span> <span class="s1">&#39;-&#39;</span><span class="p">:</span> <span class="k">return</span> <span class="s1">&#39; &#39;</span>
<span class="gp">... </span>    <span class="k">else</span><span class="p">:</span> <span class="k">return</span> <span class="s1">&#39;-&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">re</span><span class="o">.</span><span class="n">sub</span><span class="p">(</span><span class="s1">&#39;-{1,2}&#39;</span><span class="p">,</span> <span class="n">dashrepl</span><span class="p">,</span> <span class="s1">&#39;pro----gram-files&#39;</span><span class="p">)</span>
<span class="go">&#39;pro--gram files&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">re</span><span class="o">.</span><span class="n">sub</span><span class="p">(</span><span class="sa">r</span><span class="s1">&#39;\sAND\s&#39;</span><span class="p">,</span> <span class="s1">&#39; &amp; &#39;</span><span class="p">,</span> <span class="s1">&#39;Baked Beans And Spam&#39;</span><span class="p">,</span> <span class="n">flags</span><span class="o">=</span><span class="n">re</span><span class="o">.</span><span class="n">IGNORECASE</span><span class="p">)</span>
<span class="go">&#39;Baked Beans &amp; Spam&#39;</span>
</pre></div>
</div>
<p>The pattern may be a string or a <a class="reference internal" href="#re-objects"><span class="std std-ref">pattern object</span></a>.</p>
<p>The optional argument <em>count</em> is the maximum number of pattern occurrences to be
replaced; <em>count</em> must be a non-negative integer.  If omitted or zero, all
occurrences will be replaced. Empty matches for the pattern are replaced only
when not adjacent to a previous match, so <code class="docutils literal notranslate"><span class="pre">sub('x*',</span> <span class="pre">'-',</span> <span class="pre">'abc')</span></code> returns
<code class="docutils literal notranslate"><span class="pre">'-a-b-c-'</span></code>.</p>
<p>In string-type <em>repl</em> arguments, in addition to the character escapes and
backreferences described above,
<code class="docutils literal notranslate"><span class="pre">\g&lt;name&gt;</span></code> will use the substring matched by the group named <code class="docutils literal notranslate"><span class="pre">name</span></code>, as
defined by the <code class="docutils literal notranslate"><span class="pre">(?P&lt;name&gt;...)</span></code> syntax. <code class="docutils literal notranslate"><span class="pre">\g&lt;number&gt;</span></code> uses the corresponding
group number; <code class="docutils literal notranslate"><span class="pre">\g&lt;2&gt;</span></code> is therefore equivalent to <code class="docutils literal notranslate"><span class="pre">\2</span></code>, but isn't ambiguous
in a replacement such as <code class="docutils literal notranslate"><span class="pre">\g&lt;2&gt;0</span></code>.  <code class="docutils literal notranslate"><span class="pre">\20</span></code> would be interpreted as a
reference to group 20, not a reference to group 2 followed by the literal
character <code class="docutils literal notranslate"><span class="pre">'0'</span></code>.  The backreference <code class="docutils literal notranslate"><span class="pre">\g&lt;0&gt;</span></code> substitutes in the entire
substring matched by the RE.</p>
<div class="versionchanged">
<p><span class="versionmodified">在 3.1 版更改: </span>Added the optional flags argument.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">在 3.5 版更改: </span>Unmatched groups are replaced with an empty string.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">在 3.6 版更改: </span>Unknown escapes in <em>pattern</em> consisting of <code class="docutils literal notranslate"><span class="pre">'\'</span></code> and an ASCII letter
now are errors.</p>
</div>
<div class="deprecated-removed">
<p><span class="versionmodified">Deprecated since version 3.5, will be removed in version 3.7: </span>Unknown escapes in <em>repl</em> consisting of <code class="docutils literal notranslate"><span class="pre">'\'</span></code> and an ASCII letter now raise
a deprecation warning and will be forbidden in Python 3.7.</p>
</div>
</dd></dl>

<dl class="function">
<dt id="re.subn">
<code class="descclassname">re.</code><code class="descname">subn</code><span class="sig-paren">(</span><em>pattern</em>, <em>repl</em>, <em>string</em>, <em>count=0</em>, <em>flags=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.subn" title="永久链接至目标">¶</a></dt>
<dd><p>Perform the same operation as <a class="reference internal" href="#re.sub" title="re.sub"><code class="xref py py-func docutils literal notranslate"><span class="pre">sub()</span></code></a>, but return a tuple <code class="docutils literal notranslate"><span class="pre">(new_string,</span>
<span class="pre">number_of_subs_made)</span></code>.</p>
<div class="versionchanged">
<p><span class="versionmodified">在 3.1 版更改: </span>Added the optional flags argument.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">在 3.5 版更改: </span>Unmatched groups are replaced with an empty string.</p>
</div>
</dd></dl>

<dl class="function">
<dt id="re.escape">
<code class="descclassname">re.</code><code class="descname">escape</code><span class="sig-paren">(</span><em>pattern</em><span class="sig-paren">)</span><a class="headerlink" href="#re.escape" title="永久链接至目标">¶</a></dt>
<dd><p>Escape all the characters in <em>pattern</em> except ASCII letters, numbers and <code class="docutils literal notranslate"><span class="pre">'_'</span></code>.
This is useful if you want to match an arbitrary literal string that may
have regular expression metacharacters in it.  For example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="nb">print</span><span class="p">(</span><span class="n">re</span><span class="o">.</span><span class="n">escape</span><span class="p">(</span><span class="s1">&#39;python.exe&#39;</span><span class="p">))</span>
<span class="go">python\.exe</span>

<span class="gp">&gt;&gt;&gt; </span><span class="n">legal_chars</span> <span class="o">=</span> <span class="n">string</span><span class="o">.</span><span class="n">ascii_lowercase</span> <span class="o">+</span> <span class="n">string</span><span class="o">.</span><span class="n">digits</span> <span class="o">+</span> <span class="s2">&quot;!#$%&amp;&#39;*+-.^_`|~:&quot;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="nb">print</span><span class="p">(</span><span class="s1">&#39;[</span><span class="si">%s</span><span class="s1">]+&#39;</span> <span class="o">%</span> <span class="n">re</span><span class="o">.</span><span class="n">escape</span><span class="p">(</span><span class="n">legal_chars</span><span class="p">))</span>
<span class="go">[abcdefghijklmnopqrstuvwxyz0123456789\!\#\$\%\&amp;\&#39;\*\+\-\.\^_\`\|\~\:]+</span>

<span class="gp">&gt;&gt;&gt; </span><span class="n">operators</span> <span class="o">=</span> <span class="p">[</span><span class="s1">&#39;+&#39;</span><span class="p">,</span> <span class="s1">&#39;-&#39;</span><span class="p">,</span> <span class="s1">&#39;*&#39;</span><span class="p">,</span> <span class="s1">&#39;/&#39;</span><span class="p">,</span> <span class="s1">&#39;**&#39;</span><span class="p">]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="nb">print</span><span class="p">(</span><span class="s1">&#39;|&#39;</span><span class="o">.</span><span class="n">join</span><span class="p">(</span><span class="nb">map</span><span class="p">(</span><span class="n">re</span><span class="o">.</span><span class="n">escape</span><span class="p">,</span> <span class="nb">sorted</span><span class="p">(</span><span class="n">operators</span><span class="p">,</span> <span class="n">reverse</span><span class="o">=</span><span class="kc">True</span><span class="p">))))</span>
<span class="go">\/|\-|\+|\*\*|\*</span>
</pre></div>
</div>
<p>This functions must not be used for the replacement string in <a class="reference internal" href="#re.sub" title="re.sub"><code class="xref py py-func docutils literal notranslate"><span class="pre">sub()</span></code></a>
and <a class="reference internal" href="#re.subn" title="re.subn"><code class="xref py py-func docutils literal notranslate"><span class="pre">subn()</span></code></a>, only backslashes should be escaped.  For example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">digits_re</span> <span class="o">=</span> <span class="sa">r</span><span class="s1">&#39;\d+&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">sample</span> <span class="o">=</span> <span class="s1">&#39;/usr/sbin/sendmail - 0 errors, 12 warnings&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="nb">print</span><span class="p">(</span><span class="n">re</span><span class="o">.</span><span class="n">sub</span><span class="p">(</span><span class="n">digits_re</span><span class="p">,</span> <span class="n">digits_re</span><span class="o">.</span><span class="n">replace</span><span class="p">(</span><span class="s1">&#39;</span><span class="se">\\</span><span class="s1">&#39;</span><span class="p">,</span> <span class="sa">r</span><span class="s1">&#39;</span><span class="se">\\</span><span class="s1">&#39;</span><span class="p">),</span> <span class="n">sample</span><span class="p">))</span>
<span class="go">/usr/sbin/sendmail - \d+ errors, \d+ warnings</span>
</pre></div>
</div>
<div class="versionchanged">
<p><span class="versionmodified">在 3.3 版更改: </span>The <code class="docutils literal notranslate"><span class="pre">'_'</span></code> character is no longer escaped.</p>
</div>
</dd></dl>

<dl class="function">
<dt id="re.purge">
<code class="descclassname">re.</code><code class="descname">purge</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#re.purge" title="永久链接至目标">¶</a></dt>
<dd><p>Clear the regular expression cache.</p>
</dd></dl>

<dl class="exception">
<dt id="re.error">
<em class="property">exception </em><code class="descclassname">re.</code><code class="descname">error</code><span class="sig-paren">(</span><em>msg</em>, <em>pattern=None</em>, <em>pos=None</em><span class="sig-paren">)</span><a class="headerlink" href="#re.error" title="永久链接至目标">¶</a></dt>
<dd><p>Exception raised when a string passed to one of the functions here is not a
valid regular expression (for example, it might contain unmatched parentheses)
or when some other error occurs during compilation or matching.  It is never an
error if a string contains no match for a pattern.  The error instance has
the following additional attributes:</p>
<dl class="attribute">
<dt id="re.error.msg">
<code class="descname">msg</code><a class="headerlink" href="#re.error.msg" title="永久链接至目标">¶</a></dt>
<dd><p>The unformatted error message.</p>
</dd></dl>

<dl class="attribute">
<dt id="re.error.pattern">
<code class="descname">pattern</code><a class="headerlink" href="#re.error.pattern" title="永久链接至目标">¶</a></dt>
<dd><p>The regular expression pattern.</p>
</dd></dl>

<dl class="attribute">
<dt id="re.error.pos">
<code class="descname">pos</code><a class="headerlink" href="#re.error.pos" title="永久链接至目标">¶</a></dt>
<dd><p>The index in <em>pattern</em> where compilation failed (may be <code class="docutils literal notranslate"><span class="pre">None</span></code>).</p>
</dd></dl>

<dl class="attribute">
<dt id="re.error.lineno">
<code class="descname">lineno</code><a class="headerlink" href="#re.error.lineno" title="永久链接至目标">¶</a></dt>
<dd><p>The line corresponding to <em>pos</em> (may be <code class="docutils literal notranslate"><span class="pre">None</span></code>).</p>
</dd></dl>

<dl class="attribute">
<dt id="re.error.colno">
<code class="descname">colno</code><a class="headerlink" href="#re.error.colno" title="永久链接至目标">¶</a></dt>
<dd><p>The column corresponding to <em>pos</em> (may be <code class="docutils literal notranslate"><span class="pre">None</span></code>).</p>
</dd></dl>

<div class="versionchanged">
<p><span class="versionmodified">在 3.5 版更改: </span>Added additional attributes.</p>
</div>
</dd></dl>

</div>
<div class="section" id="regular-expression-objects">
<span id="re-objects"></span><h2>6.2.3. Regular Expression Objects<a class="headerlink" href="#regular-expression-objects" title="永久链接至标题">¶</a></h2>
<p>Compiled regular expression objects support the following methods and
attributes:</p>
<dl class="method">
<dt id="re.regex.search">
<code class="descclassname">regex.</code><code class="descname">search</code><span class="sig-paren">(</span><em>string</em><span class="optional">[</span>, <em>pos</em><span class="optional">[</span>, <em>endpos</em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.regex.search" title="永久链接至目标">¶</a></dt>
<dd><p>Scan through <em>string</em> looking for the first location where this regular
expression produces a match, and return a corresponding <a class="reference internal" href="#match-objects"><span class="std std-ref">match object</span></a>.  Return <code class="docutils literal notranslate"><span class="pre">None</span></code> if no position in the string matches the
pattern; note that this is different from finding a zero-length match at some
point in the string.</p>
<p>The optional second parameter <em>pos</em> gives an index in the string where the
search is to start; it defaults to <code class="docutils literal notranslate"><span class="pre">0</span></code>.  This is not completely equivalent to
slicing the string; the <code class="docutils literal notranslate"><span class="pre">'^'</span></code> pattern character matches at the real beginning
of the string and at positions just after a newline, but not necessarily at the
index where the search is to start.</p>
<p>The optional parameter <em>endpos</em> limits how far the string will be searched; it
will be as if the string is <em>endpos</em> characters long, so only the characters
from <em>pos</em> to <code class="docutils literal notranslate"><span class="pre">endpos</span> <span class="pre">-</span> <span class="pre">1</span></code> will be searched for a match.  If <em>endpos</em> is less
than <em>pos</em>, no match will be found; otherwise, if <em>rx</em> is a compiled regular
expression object, <code class="docutils literal notranslate"><span class="pre">rx.search(string,</span> <span class="pre">0,</span> <span class="pre">50)</span></code> is equivalent to
<code class="docutils literal notranslate"><span class="pre">rx.search(string[:50],</span> <span class="pre">0)</span></code>.</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">pattern</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="s2">&quot;d&quot;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">pattern</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s2">&quot;dog&quot;</span><span class="p">)</span>     <span class="c1"># Match at index 0</span>
<span class="go">&lt;_sre.SRE_Match object; span=(0, 1), match=&#39;d&#39;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">pattern</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s2">&quot;dog&quot;</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span>  <span class="c1"># No match; search doesn&#39;t include the &quot;d&quot;</span>
</pre></div>
</div>
</dd></dl>

<dl class="method">
<dt id="re.regex.match">
<code class="descclassname">regex.</code><code class="descname">match</code><span class="sig-paren">(</span><em>string</em><span class="optional">[</span>, <em>pos</em><span class="optional">[</span>, <em>endpos</em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.regex.match" title="永久链接至目标">¶</a></dt>
<dd><p>If zero or more characters at the <em>beginning</em> of <em>string</em> match this regular
expression, return a corresponding <a class="reference internal" href="#match-objects"><span class="std std-ref">match object</span></a>.
Return <code class="docutils literal notranslate"><span class="pre">None</span></code> if the string does not match the pattern; note that this is
different from a zero-length match.</p>
<p>The optional <em>pos</em> and <em>endpos</em> parameters have the same meaning as for the
<a class="reference internal" href="#re.regex.search" title="re.regex.search"><code class="xref py py-meth docutils literal notranslate"><span class="pre">search()</span></code></a> method.</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">pattern</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="s2">&quot;o&quot;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">pattern</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">&quot;dog&quot;</span><span class="p">)</span>      <span class="c1"># No match as &quot;o&quot; is not at the start of &quot;dog&quot;.</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">pattern</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">&quot;dog&quot;</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span>   <span class="c1"># Match as &quot;o&quot; is the 2nd character of &quot;dog&quot;.</span>
<span class="go">&lt;_sre.SRE_Match object; span=(1, 2), match=&#39;o&#39;&gt;</span>
</pre></div>
</div>
<p>If you want to locate a match anywhere in <em>string</em>, use
<a class="reference internal" href="#re.regex.search" title="re.regex.search"><code class="xref py py-meth docutils literal notranslate"><span class="pre">search()</span></code></a> instead (see also <a class="reference internal" href="#search-vs-match"><span class="std std-ref">search() vs. match()</span></a>).</p>
</dd></dl>

<dl class="method">
<dt id="re.regex.fullmatch">
<code class="descclassname">regex.</code><code class="descname">fullmatch</code><span class="sig-paren">(</span><em>string</em><span class="optional">[</span>, <em>pos</em><span class="optional">[</span>, <em>endpos</em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.regex.fullmatch" title="永久链接至目标">¶</a></dt>
<dd><p>If the whole <em>string</em> matches this regular expression, return a corresponding
<a class="reference internal" href="#match-objects"><span class="std std-ref">match object</span></a>.  Return <code class="docutils literal notranslate"><span class="pre">None</span></code> if the string does not
match the pattern; note that this is different from a zero-length match.</p>
<p>The optional <em>pos</em> and <em>endpos</em> parameters have the same meaning as for the
<a class="reference internal" href="#re.regex.search" title="re.regex.search"><code class="xref py py-meth docutils literal notranslate"><span class="pre">search()</span></code></a> method.</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">pattern</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="s2">&quot;o[gh]&quot;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">pattern</span><span class="o">.</span><span class="n">fullmatch</span><span class="p">(</span><span class="s2">&quot;dog&quot;</span><span class="p">)</span>      <span class="c1"># No match as &quot;o&quot; is not at the start of &quot;dog&quot;.</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">pattern</span><span class="o">.</span><span class="n">fullmatch</span><span class="p">(</span><span class="s2">&quot;ogre&quot;</span><span class="p">)</span>     <span class="c1"># No match as not the full string matches.</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">pattern</span><span class="o">.</span><span class="n">fullmatch</span><span class="p">(</span><span class="s2">&quot;doggie&quot;</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">3</span><span class="p">)</span>   <span class="c1"># Matches within given limits.</span>
<span class="go">&lt;_sre.SRE_Match object; span=(1, 3), match=&#39;og&#39;&gt;</span>
</pre></div>
</div>
<div class="versionadded">
<p><span class="versionmodified">3.4 新版功能.</span></p>
</div>
</dd></dl>

<dl class="method">
<dt id="re.regex.split">
<code class="descclassname">regex.</code><code class="descname">split</code><span class="sig-paren">(</span><em>string</em>, <em>maxsplit=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.regex.split" title="永久链接至目标">¶</a></dt>
<dd><p>Identical to the <a class="reference internal" href="#re.split" title="re.split"><code class="xref py py-func docutils literal notranslate"><span class="pre">split()</span></code></a> function, using the compiled pattern.</p>
</dd></dl>

<dl class="method">
<dt id="re.regex.findall">
<code class="descclassname">regex.</code><code class="descname">findall</code><span class="sig-paren">(</span><em>string</em><span class="optional">[</span>, <em>pos</em><span class="optional">[</span>, <em>endpos</em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.regex.findall" title="永久链接至目标">¶</a></dt>
<dd><p>Similar to the <a class="reference internal" href="#re.findall" title="re.findall"><code class="xref py py-func docutils literal notranslate"><span class="pre">findall()</span></code></a> function, using the compiled pattern, but
also accepts optional <em>pos</em> and <em>endpos</em> parameters that limit the search
region like for <a class="reference internal" href="#re.search" title="re.search"><code class="xref py py-meth docutils literal notranslate"><span class="pre">search()</span></code></a>.</p>
</dd></dl>

<dl class="method">
<dt id="re.regex.finditer">
<code class="descclassname">regex.</code><code class="descname">finditer</code><span class="sig-paren">(</span><em>string</em><span class="optional">[</span>, <em>pos</em><span class="optional">[</span>, <em>endpos</em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.regex.finditer" title="永久链接至目标">¶</a></dt>
<dd><p>Similar to the <a class="reference internal" href="#re.finditer" title="re.finditer"><code class="xref py py-func docutils literal notranslate"><span class="pre">finditer()</span></code></a> function, using the compiled pattern, but
also accepts optional <em>pos</em> and <em>endpos</em> parameters that limit the search
region like for <a class="reference internal" href="#re.search" title="re.search"><code class="xref py py-meth docutils literal notranslate"><span class="pre">search()</span></code></a>.</p>
</dd></dl>

<dl class="method">
<dt id="re.regex.sub">
<code class="descclassname">regex.</code><code class="descname">sub</code><span class="sig-paren">(</span><em>repl</em>, <em>string</em>, <em>count=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.regex.sub" title="永久链接至目标">¶</a></dt>
<dd><p>Identical to the <a class="reference internal" href="#re.sub" title="re.sub"><code class="xref py py-func docutils literal notranslate"><span class="pre">sub()</span></code></a> function, using the compiled pattern.</p>
</dd></dl>

<dl class="method">
<dt id="re.regex.subn">
<code class="descclassname">regex.</code><code class="descname">subn</code><span class="sig-paren">(</span><em>repl</em>, <em>string</em>, <em>count=0</em><span class="sig-paren">)</span><a class="headerlink" href="#re.regex.subn" title="永久链接至目标">¶</a></dt>
<dd><p>Identical to the <a class="reference internal" href="#re.subn" title="re.subn"><code class="xref py py-func docutils literal notranslate"><span class="pre">subn()</span></code></a> function, using the compiled pattern.</p>
</dd></dl>

<dl class="attribute">
<dt id="re.regex.flags">
<code class="descclassname">regex.</code><code class="descname">flags</code><a class="headerlink" href="#re.regex.flags" title="永久链接至目标">¶</a></dt>
<dd><p>The regex matching flags.  This is a combination of the flags given to
<a class="reference internal" href="#re.compile" title="re.compile"><code class="xref py py-func docutils literal notranslate"><span class="pre">compile()</span></code></a>, any <code class="docutils literal notranslate"><span class="pre">(?...)</span></code> inline flags in the pattern, and implicit
flags such as <code class="xref py py-data docutils literal notranslate"><span class="pre">UNICODE</span></code> if the pattern is a Unicode string.</p>
</dd></dl>

<dl class="attribute">
<dt id="re.regex.groups">
<code class="descclassname">regex.</code><code class="descname">groups</code><a class="headerlink" href="#re.regex.groups" title="永久链接至目标">¶</a></dt>
<dd><p>The number of capturing groups in the pattern.</p>
</dd></dl>

<dl class="attribute">
<dt id="re.regex.groupindex">
<code class="descclassname">regex.</code><code class="descname">groupindex</code><a class="headerlink" href="#re.regex.groupindex" title="永久链接至目标">¶</a></dt>
<dd><p>A dictionary mapping any symbolic group names defined by <code class="docutils literal notranslate"><span class="pre">(?P&lt;id&gt;)</span></code> to group
numbers.  The dictionary is empty if no symbolic groups were used in the
pattern.</p>
</dd></dl>

<dl class="attribute">
<dt id="re.regex.pattern">
<code class="descclassname">regex.</code><code class="descname">pattern</code><a class="headerlink" href="#re.regex.pattern" title="永久链接至目标">¶</a></dt>
<dd><p>The pattern string from which the RE object was compiled.</p>
</dd></dl>

</div>
<div class="section" id="match-objects">
<span id="id2"></span><h2>6.2.4. Match Objects<a class="headerlink" href="#match-objects" title="永久链接至标题">¶</a></h2>
<p>Match objects always have a boolean value of <code class="docutils literal notranslate"><span class="pre">True</span></code>.
Since <a class="reference internal" href="#re.regex.match" title="re.regex.match"><code class="xref py py-meth docutils literal notranslate"><span class="pre">match()</span></code></a> and <a class="reference internal" href="#re.regex.search" title="re.regex.search"><code class="xref py py-meth docutils literal notranslate"><span class="pre">search()</span></code></a> return <code class="docutils literal notranslate"><span class="pre">None</span></code>
when there is no match, you can test whether there was a match with a simple
<code class="docutils literal notranslate"><span class="pre">if</span></code> statement:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">match</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="n">pattern</span><span class="p">,</span> <span class="n">string</span><span class="p">)</span>
<span class="k">if</span> <span class="n">match</span><span class="p">:</span>
    <span class="n">process</span><span class="p">(</span><span class="n">match</span><span class="p">)</span>
</pre></div>
</div>
<p>Match objects support the following methods and attributes:</p>
<dl class="method">
<dt id="re.match.expand">
<code class="descclassname">match.</code><code class="descname">expand</code><span class="sig-paren">(</span><em>template</em><span class="sig-paren">)</span><a class="headerlink" href="#re.match.expand" title="永久链接至目标">¶</a></dt>
<dd><p>Return the string obtained by doing backslash substitution on the template
string <em>template</em>, as done by the <a class="reference internal" href="#re.regex.sub" title="re.regex.sub"><code class="xref py py-meth docutils literal notranslate"><span class="pre">sub()</span></code></a> method.
Escapes such as <code class="docutils literal notranslate"><span class="pre">\n</span></code> are converted to the appropriate characters,
and numeric backreferences (<code class="docutils literal notranslate"><span class="pre">\1</span></code>, <code class="docutils literal notranslate"><span class="pre">\2</span></code>) and named backreferences
(<code class="docutils literal notranslate"><span class="pre">\g&lt;1&gt;</span></code>, <code class="docutils literal notranslate"><span class="pre">\g&lt;name&gt;</span></code>) are replaced by the contents of the
corresponding group.</p>
<div class="versionchanged">
<p><span class="versionmodified">在 3.5 版更改: </span>Unmatched groups are replaced with an empty string.</p>
</div>
</dd></dl>

<dl class="method">
<dt id="re.match.group">
<code class="descclassname">match.</code><code class="descname">group</code><span class="sig-paren">(</span><span class="optional">[</span><em>group1</em>, <em>...</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.match.group" title="永久链接至目标">¶</a></dt>
<dd><p>Returns one or more subgroups of the match.  If there is a single argument, the
result is a single string; if there are multiple arguments, the result is a
tuple with one item per argument. Without arguments, <em>group1</em> defaults to zero
(the whole match is returned). If a <em>groupN</em> argument is zero, the corresponding
return value is the entire matching string; if it is in the inclusive range
[1..99], it is the string matching the corresponding parenthesized group.  If a
group number is negative or larger than the number of groups defined in the
pattern, an <a class="reference internal" href="exceptions.html#IndexError" title="IndexError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">IndexError</span></code></a> exception is raised. If a group is contained in a
part of the pattern that did not match, the corresponding result is <code class="docutils literal notranslate"><span class="pre">None</span></code>.
If a group is contained in a part of the pattern that matched multiple times,
the last match is returned.</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">&quot;(\w+) (\w+)&quot;</span><span class="p">,</span> <span class="s2">&quot;Isaac Newton, physicist&quot;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span>       <span class="c1"># The entire match</span>
<span class="go">&#39;Isaac Newton&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>       <span class="c1"># The first parenthesized subgroup.</span>
<span class="go">&#39;Isaac&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">2</span><span class="p">)</span>       <span class="c1"># The second parenthesized subgroup.</span>
<span class="go">&#39;Newton&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">)</span>    <span class="c1"># Multiple arguments give us a tuple.</span>
<span class="go">(&#39;Isaac&#39;, &#39;Newton&#39;)</span>
</pre></div>
</div>
<p>If the regular expression uses the <code class="docutils literal notranslate"><span class="pre">(?P&lt;name&gt;...)</span></code> syntax, the <em>groupN</em>
arguments may also be strings identifying groups by their group name.  If a
string argument is not used as a group name in the pattern, an <a class="reference internal" href="exceptions.html#IndexError" title="IndexError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">IndexError</span></code></a>
exception is raised.</p>
<p>A moderately complicated example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">&quot;(?P&lt;first_name&gt;\w+) (?P&lt;last_name&gt;\w+)&quot;</span><span class="p">,</span> <span class="s2">&quot;Malcolm Reynolds&quot;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="s1">&#39;first_name&#39;</span><span class="p">)</span>
<span class="go">&#39;Malcolm&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="s1">&#39;last_name&#39;</span><span class="p">)</span>
<span class="go">&#39;Reynolds&#39;</span>
</pre></div>
</div>
<p>Named groups can also be referred to by their index:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="go">&#39;Malcolm&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">2</span><span class="p">)</span>
<span class="go">&#39;Reynolds&#39;</span>
</pre></div>
</div>
<p>If a group matches multiple times, only the last match is accessible:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">&quot;(..)+&quot;</span><span class="p">,</span> <span class="s2">&quot;a1b2c3&quot;</span><span class="p">)</span>  <span class="c1"># Matches 3 times.</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>                        <span class="c1"># Returns only the last match.</span>
<span class="go">&#39;c3&#39;</span>
</pre></div>
</div>
</dd></dl>

<dl class="method">
<dt id="re.match.__getitem__">
<code class="descclassname">match.</code><code class="descname">__getitem__</code><span class="sig-paren">(</span><em>g</em><span class="sig-paren">)</span><a class="headerlink" href="#re.match.__getitem__" title="永久链接至目标">¶</a></dt>
<dd><p>This is identical to <code class="docutils literal notranslate"><span class="pre">m.group(g)</span></code>.  This allows easier access to
an individual group from a match:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">&quot;(\w+) (\w+)&quot;</span><span class="p">,</span> <span class="s2">&quot;Isaac Newton, physicist&quot;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span>       <span class="c1"># The entire match</span>
<span class="go">&#39;Isaac Newton&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span>       <span class="c1"># The first parenthesized subgroup.</span>
<span class="go">&#39;Isaac&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="p">[</span><span class="mi">2</span><span class="p">]</span>       <span class="c1"># The second parenthesized subgroup.</span>
<span class="go">&#39;Newton&#39;</span>
</pre></div>
</div>
<div class="versionadded">
<p><span class="versionmodified">3.6 新版功能.</span></p>
</div>
</dd></dl>

<dl class="method">
<dt id="re.match.groups">
<code class="descclassname">match.</code><code class="descname">groups</code><span class="sig-paren">(</span><em>default=None</em><span class="sig-paren">)</span><a class="headerlink" href="#re.match.groups" title="永久链接至目标">¶</a></dt>
<dd><p>Return a tuple containing all the subgroups of the match, from 1 up to however
many groups are in the pattern.  The <em>default</em> argument is used for groups that
did not participate in the match; it defaults to <code class="docutils literal notranslate"><span class="pre">None</span></code>.</p>
<p>For example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">&quot;(\d+)\.(\d+)&quot;</span><span class="p">,</span> <span class="s2">&quot;24.1632&quot;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="o">.</span><span class="n">groups</span><span class="p">()</span>
<span class="go">(&#39;24&#39;, &#39;1632&#39;)</span>
</pre></div>
</div>
<p>If we make the decimal place and everything after it optional, not all groups
might participate in the match.  These groups will default to <code class="docutils literal notranslate"><span class="pre">None</span></code> unless
the <em>default</em> argument is given:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">&quot;(\d+)\.?(\d+)?&quot;</span><span class="p">,</span> <span class="s2">&quot;24&quot;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="o">.</span><span class="n">groups</span><span class="p">()</span>      <span class="c1"># Second group defaults to None.</span>
<span class="go">(&#39;24&#39;, None)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="o">.</span><span class="n">groups</span><span class="p">(</span><span class="s1">&#39;0&#39;</span><span class="p">)</span>   <span class="c1"># Now, the second group defaults to &#39;0&#39;.</span>
<span class="go">(&#39;24&#39;, &#39;0&#39;)</span>
</pre></div>
</div>
</dd></dl>

<dl class="method">
<dt id="re.match.groupdict">
<code class="descclassname">match.</code><code class="descname">groupdict</code><span class="sig-paren">(</span><em>default=None</em><span class="sig-paren">)</span><a class="headerlink" href="#re.match.groupdict" title="永久链接至目标">¶</a></dt>
<dd><p>Return a dictionary containing all the <em>named</em> subgroups of the match, keyed by
the subgroup name.  The <em>default</em> argument is used for groups that did not
participate in the match; it defaults to <code class="docutils literal notranslate"><span class="pre">None</span></code>.  For example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">&quot;(?P&lt;first_name&gt;\w+) (?P&lt;last_name&gt;\w+)&quot;</span><span class="p">,</span> <span class="s2">&quot;Malcolm Reynolds&quot;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span><span class="o">.</span><span class="n">groupdict</span><span class="p">()</span>
<span class="go">{&#39;first_name&#39;: &#39;Malcolm&#39;, &#39;last_name&#39;: &#39;Reynolds&#39;}</span>
</pre></div>
</div>
</dd></dl>

<dl class="method">
<dt id="re.match.start">
<code class="descclassname">match.</code><code class="descname">start</code><span class="sig-paren">(</span><span class="optional">[</span><em>group</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.match.start" title="永久链接至目标">¶</a></dt>
<dt id="re.match.end">
<code class="descclassname">match.</code><code class="descname">end</code><span class="sig-paren">(</span><span class="optional">[</span><em>group</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.match.end" title="永久链接至目标">¶</a></dt>
<dd><p>Return the indices of the start and end of the substring matched by <em>group</em>;
<em>group</em> defaults to zero (meaning the whole matched substring). Return <code class="docutils literal notranslate"><span class="pre">-1</span></code> if
<em>group</em> exists but did not contribute to the match.  For a match object <em>m</em>, and
a group <em>g</em> that did contribute to the match, the substring matched by group <em>g</em>
(equivalent to <code class="docutils literal notranslate"><span class="pre">m.group(g)</span></code>) is</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">m</span><span class="o">.</span><span class="n">string</span><span class="p">[</span><span class="n">m</span><span class="o">.</span><span class="n">start</span><span class="p">(</span><span class="n">g</span><span class="p">):</span><span class="n">m</span><span class="o">.</span><span class="n">end</span><span class="p">(</span><span class="n">g</span><span class="p">)]</span>
</pre></div>
</div>
<p>Note that <code class="docutils literal notranslate"><span class="pre">m.start(group)</span></code> will equal <code class="docutils literal notranslate"><span class="pre">m.end(group)</span></code> if <em>group</em> matched a
null string.  For example, after <code class="docutils literal notranslate"><span class="pre">m</span> <span class="pre">=</span> <span class="pre">re.search('b(c?)',</span> <span class="pre">'cba')</span></code>,
<code class="docutils literal notranslate"><span class="pre">m.start(0)</span></code> is 1, <code class="docutils literal notranslate"><span class="pre">m.end(0)</span></code> is 2, <code class="docutils literal notranslate"><span class="pre">m.start(1)</span></code> and <code class="docutils literal notranslate"><span class="pre">m.end(1)</span></code> are both
2, and <code class="docutils literal notranslate"><span class="pre">m.start(2)</span></code> raises an <a class="reference internal" href="exceptions.html#IndexError" title="IndexError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">IndexError</span></code></a> exception.</p>
<p>An example that will remove <em>remove_this</em> from email addresses:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">email</span> <span class="o">=</span> <span class="s2">&quot;tony@tiremove_thisger.net&quot;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">m</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s2">&quot;remove_this&quot;</span><span class="p">,</span> <span class="n">email</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">email</span><span class="p">[:</span><span class="n">m</span><span class="o">.</span><span class="n">start</span><span class="p">()]</span> <span class="o">+</span> <span class="n">email</span><span class="p">[</span><span class="n">m</span><span class="o">.</span><span class="n">end</span><span class="p">():]</span>
<span class="go">&#39;tony@tiger.net&#39;</span>
</pre></div>
</div>
</dd></dl>

<dl class="method">
<dt id="re.match.span">
<code class="descclassname">match.</code><code class="descname">span</code><span class="sig-paren">(</span><span class="optional">[</span><em>group</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#re.match.span" title="永久链接至目标">¶</a></dt>
<dd><p>For a match <em>m</em>, return the 2-tuple <code class="docutils literal notranslate"><span class="pre">(m.start(group),</span> <span class="pre">m.end(group))</span></code>. Note
that if <em>group</em> did not contribute to the match, this is <code class="docutils literal notranslate"><span class="pre">(-1,</span> <span class="pre">-1)</span></code>.
<em>group</em> defaults to zero, the entire match.</p>
</dd></dl>

<dl class="attribute">
<dt id="re.match.pos">
<code class="descclassname">match.</code><code class="descname">pos</code><a class="headerlink" href="#re.match.pos" title="永久链接至目标">¶</a></dt>
<dd><p>The value of <em>pos</em> which was passed to the <a class="reference internal" href="#re.regex.search" title="re.regex.search"><code class="xref py py-meth docutils literal notranslate"><span class="pre">search()</span></code></a> or
<a class="reference internal" href="#re.regex.match" title="re.regex.match"><code class="xref py py-meth docutils literal notranslate"><span class="pre">match()</span></code></a> method of a <a class="reference internal" href="#re-objects"><span class="std std-ref">regex object</span></a>.  This is
the index into the string at which the RE engine started looking for a match.</p>
</dd></dl>

<dl class="attribute">
<dt id="re.match.endpos">
<code class="descclassname">match.</code><code class="descname">endpos</code><a class="headerlink" href="#re.match.endpos" title="永久链接至目标">¶</a></dt>
<dd><p>The value of <em>endpos</em> which was passed to the <a class="reference internal" href="#re.regex.search" title="re.regex.search"><code class="xref py py-meth docutils literal notranslate"><span class="pre">search()</span></code></a> or
<a class="reference internal" href="#re.regex.match" title="re.regex.match"><code class="xref py py-meth docutils literal notranslate"><span class="pre">match()</span></code></a> method of a <a class="reference internal" href="#re-objects"><span class="std std-ref">regex object</span></a>.  This is
the index into the string beyond which the RE engine will not go.</p>
</dd></dl>

<dl class="attribute">
<dt id="re.match.lastindex">
<code class="descclassname">match.</code><code class="descname">lastindex</code><a class="headerlink" href="#re.match.lastindex" title="永久链接至目标">¶</a></dt>
<dd><p>The integer index of the last matched capturing group, or <code class="docutils literal notranslate"><span class="pre">None</span></code> if no group
was matched at all. For example, the expressions <code class="docutils literal notranslate"><span class="pre">(a)b</span></code>, <code class="docutils literal notranslate"><span class="pre">((a)(b))</span></code>, and
<code class="docutils literal notranslate"><span class="pre">((ab))</span></code> will have <code class="docutils literal notranslate"><span class="pre">lastindex</span> <span class="pre">==</span> <span class="pre">1</span></code> if applied to the string <code class="docutils literal notranslate"><span class="pre">'ab'</span></code>, while
the expression <code class="docutils literal notranslate"><span class="pre">(a)(b)</span></code> will have <code class="docutils literal notranslate"><span class="pre">lastindex</span> <span class="pre">==</span> <span class="pre">2</span></code>, if applied to the same
string.</p>
</dd></dl>

<dl class="attribute">
<dt id="re.match.lastgroup">
<code class="descclassname">match.</code><code class="descname">lastgroup</code><a class="headerlink" href="#re.match.lastgroup" title="永久链接至目标">¶</a></dt>
<dd><p>The name of the last matched capturing group, or <code class="docutils literal notranslate"><span class="pre">None</span></code> if the group didn't
have a name, or if no group was matched at all.</p>
</dd></dl>

<dl class="attribute">
<dt id="re.match.re">
<code class="descclassname">match.</code><code class="descname">re</code><a class="headerlink" href="#re.match.re" title="永久链接至目标">¶</a></dt>
<dd><p>The <a class="reference internal" href="#re-objects"><span class="std std-ref">regular expression object</span></a> whose <a class="reference internal" href="#re.regex.match" title="re.regex.match"><code class="xref py py-meth docutils literal notranslate"><span class="pre">match()</span></code></a> or
<a class="reference internal" href="#re.regex.search" title="re.regex.search"><code class="xref py py-meth docutils literal notranslate"><span class="pre">search()</span></code></a> method produced this match instance.</p>
</dd></dl>

<dl class="attribute">
<dt id="re.match.string">
<code class="descclassname">match.</code><code class="descname">string</code><a class="headerlink" href="#re.match.string" title="永久链接至目标">¶</a></dt>
<dd><p>The string passed to <a class="reference internal" href="#re.regex.match" title="re.regex.match"><code class="xref py py-meth docutils literal notranslate"><span class="pre">match()</span></code></a> or <a class="reference internal" href="#re.regex.search" title="re.regex.search"><code class="xref py py-meth docutils literal notranslate"><span class="pre">search()</span></code></a>.</p>
</dd></dl>

</div>
<div class="section" id="regular-expression-examples">
<span id="re-examples"></span><h2>6.2.5. Regular Expression Examples<a class="headerlink" href="#regular-expression-examples" title="永久链接至标题">¶</a></h2>
<div class="section" id="checking-for-a-pair">
<h3>6.2.5.1. Checking for a Pair<a class="headerlink" href="#checking-for-a-pair" title="永久链接至标题">¶</a></h3>
<p>In this example, we'll use the following helper function to display match
objects a little more gracefully:</p>
<div class="highlight-python notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">displaymatch</span><span class="p">(</span><span class="n">match</span><span class="p">):</span>
    <span class="k">if</span> <span class="n">match</span> <span class="ow">is</span> <span class="bp">None</span><span class="p">:</span>
        <span class="k">return</span> <span class="bp">None</span>
    <span class="k">return</span> <span class="s1">&#39;&lt;Match: </span><span class="si">%r</span><span class="s1">, groups=</span><span class="si">%r</span><span class="s1">&gt;&#39;</span> <span class="o">%</span> <span class="p">(</span><span class="n">match</span><span class="o">.</span><span class="n">group</span><span class="p">(),</span> <span class="n">match</span><span class="o">.</span><span class="n">groups</span><span class="p">())</span>
</pre></div>
</div>
<p>Suppose you are writing a poker program where a player's hand is represented as
a 5-character string with each character representing a card, &quot;a&quot; for ace, &quot;k&quot;
for king, &quot;q&quot; for queen, &quot;j&quot; for jack, &quot;t&quot; for 10, and &quot;2&quot; through &quot;9&quot;
representing the card with that value.</p>
<p>To see if a given string is a valid hand, one could do the following:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">valid</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="sa">r</span><span class="s2">&quot;^[a2-9tjqk]</span><span class="si">{5}</span><span class="s2">$&quot;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">displaymatch</span><span class="p">(</span><span class="n">valid</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">&quot;akt5q&quot;</span><span class="p">))</span>  <span class="c1"># Valid.</span>
<span class="go">&quot;&lt;Match: &#39;akt5q&#39;, groups=()&gt;&quot;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">displaymatch</span><span class="p">(</span><span class="n">valid</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">&quot;akt5e&quot;</span><span class="p">))</span>  <span class="c1"># Invalid.</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">displaymatch</span><span class="p">(</span><span class="n">valid</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">&quot;akt&quot;</span><span class="p">))</span>    <span class="c1"># Invalid.</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">displaymatch</span><span class="p">(</span><span class="n">valid</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">&quot;727ak&quot;</span><span class="p">))</span>  <span class="c1"># Valid.</span>
<span class="go">&quot;&lt;Match: &#39;727ak&#39;, groups=()&gt;&quot;</span>
</pre></div>
</div>
<p>That last hand, <code class="docutils literal notranslate"><span class="pre">&quot;727ak&quot;</span></code>, contained a pair, or two of the same valued cards.
To match this with a regular expression, one could use backreferences as such:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">pair</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">compile</span><span class="p">(</span><span class="sa">r</span><span class="s2">&quot;.*(.).*\1&quot;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">displaymatch</span><span class="p">(</span><span class="n">pair</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">&quot;717ak&quot;</span><span class="p">))</span>     <span class="c1"># Pair of 7s.</span>
<span class="go">&quot;&lt;Match: &#39;717&#39;, groups=(&#39;7&#39;,)&gt;&quot;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">displaymatch</span><span class="p">(</span><span class="n">pair</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">&quot;718ak&quot;</span><span class="p">))</span>     <span class="c1"># No pairs.</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">displaymatch</span><span class="p">(</span><span class="n">pair</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">&quot;354aa&quot;</span><span class="p">))</span>     <span class="c1"># Pair of aces.</span>
<span class="go">&quot;&lt;Match: &#39;354aa&#39;, groups=(&#39;a&#39;,)&gt;&quot;</span>
</pre></div>
</div>
<p>To find out what card the pair consists of, one could use the
<a class="reference internal" href="#re.match.group" title="re.match.group"><code class="xref py py-meth docutils literal notranslate"><span class="pre">group()</span></code></a> method of the match object in the following manner:</p>
<div class="highlight-pycon notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">pair</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">&quot;717ak&quot;</span><span class="p">)</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="go">&#39;7&#39;</span>

<span class="go"># Error because re.match() returns None, which doesn&#39;t have a group() method:</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">pair</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">&quot;718ak&quot;</span><span class="p">)</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="gt">Traceback (most recent call last):</span>
  File <span class="nb">&quot;&lt;pyshell#23&gt;&quot;</span>, line <span class="m">1</span>, in <span class="n">&lt;module&gt;</span>
    <span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">&quot;.*(.).*\1&quot;</span><span class="p">,</span> <span class="s2">&quot;718ak&quot;</span><span class="p">)</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="gr">AttributeError</span>: <span class="n">&#39;NoneType&#39; object has no attribute &#39;group&#39;</span>

<span class="gp">&gt;&gt;&gt; </span><span class="n">pair</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">&quot;354aa&quot;</span><span class="p">)</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="go">&#39;a&#39;</span>
</pre></div>
</div>
</div>
<div class="section" id="simulating-scanf">
<h3>6.2.5.2. Simulating scanf()<a class="headerlink" href="#simulating-scanf" title="永久链接至标题">¶</a></h3>
<p id="index-0">Python does not currently have an equivalent to <code class="xref c c-func docutils literal notranslate"><span class="pre">scanf()</span></code>.  Regular
expressions are generally more powerful, though also more verbose, than
<code class="xref c c-func docutils literal notranslate"><span class="pre">scanf()</span></code> format strings.  The table below offers some more-or-less
equivalent mappings between <code class="xref c c-func docutils literal notranslate"><span class="pre">scanf()</span></code> format tokens and regular
expressions.</p>
<table border="1" class="docutils">
<colgroup>
<col width="42%" />
<col width="58%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head"><code class="xref c c-func docutils literal notranslate"><span class="pre">scanf()</span></code> Token</th>
<th class="head">Regular Expression</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">%c</span></code></td>
<td><code class="docutils literal notranslate"><span class="pre">.</span></code></td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">%5c</span></code></td>
<td><code class="docutils literal notranslate"><span class="pre">.{5}</span></code></td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">%d</span></code></td>
<td><code class="docutils literal notranslate"><span class="pre">[-+]?\d+</span></code></td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">%e</span></code>, <code class="docutils literal notranslate"><span class="pre">%E</span></code>, <code class="docutils literal notranslate"><span class="pre">%f</span></code>, <code class="docutils literal notranslate"><span class="pre">%g</span></code></td>
<td><code class="docutils literal notranslate"><span class="pre">[-+]?(\d+(\.\d*)?|\.\d+)([eE][-+]?\d+)?</span></code></td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">%i</span></code></td>
<td><code class="docutils literal notranslate"><span class="pre">[-+]?(0[xX][\dA-Fa-f]+|0[0-7]*|\d+)</span></code></td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">%o</span></code></td>
<td><code class="docutils literal notranslate"><span class="pre">[-+]?[0-7]+</span></code></td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">%s</span></code></td>
<td><code class="docutils literal notranslate"><span class="pre">\S+</span></code></td>
</tr>
<tr class="row-odd"><td><code class="docutils literal notranslate"><span class="pre">%u</span></code></td>
<td><code class="docutils literal notranslate"><span class="pre">\d+</span></code></td>
</tr>
<tr class="row-even"><td><code class="docutils literal notranslate"><span class="pre">%x</span></code>, <code class="docutils literal notranslate"><span class="pre">%X</span></code></td>
<td><code class="docutils literal notranslate"><span class="pre">[-+]?(0[xX])?[\dA-Fa-f]+</span></code></td>
</tr>
</tbody>
</table>
<p>To extract the filename and numbers from a string like</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="o">/</span><span class="n">usr</span><span class="o">/</span><span class="n">sbin</span><span class="o">/</span><span class="n">sendmail</span> <span class="o">-</span> <span class="mi">0</span> <span class="n">errors</span><span class="p">,</span> <span class="mi">4</span> <span class="n">warnings</span>
</pre></div>
</div>
<p>you would use a <code class="xref c c-func docutils literal notranslate"><span class="pre">scanf()</span></code> format like</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="o">%</span><span class="n">s</span> <span class="o">-</span> <span class="o">%</span><span class="n">d</span> <span class="n">errors</span><span class="p">,</span> <span class="o">%</span><span class="n">d</span> <span class="n">warnings</span>
</pre></div>
</div>
<p>The equivalent regular expression would be</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="p">(</span>\<span class="n">S</span><span class="o">+</span><span class="p">)</span> <span class="o">-</span> <span class="p">(</span>\<span class="n">d</span><span class="o">+</span><span class="p">)</span> <span class="n">errors</span><span class="p">,</span> <span class="p">(</span>\<span class="n">d</span><span class="o">+</span><span class="p">)</span> <span class="n">warnings</span>
</pre></div>
</div>
</div>
<div class="section" id="search-vs-match">
<span id="id3"></span><h3>6.2.5.3. search() vs. match()<a class="headerlink" href="#search-vs-match" title="永久链接至标题">¶</a></h3>
<p>Python offers two different primitive operations based on regular expressions:
<a class="reference internal" href="#re.match" title="re.match"><code class="xref py py-func docutils literal notranslate"><span class="pre">re.match()</span></code></a> checks for a match only at the beginning of the string, while
<a class="reference internal" href="#re.search" title="re.search"><code class="xref py py-func docutils literal notranslate"><span class="pre">re.search()</span></code></a> checks for a match anywhere in the string (this is what Perl
does by default).</p>
<p>For example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">&quot;c&quot;</span><span class="p">,</span> <span class="s2">&quot;abcdef&quot;</span><span class="p">)</span>    <span class="c1"># No match</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s2">&quot;c&quot;</span><span class="p">,</span> <span class="s2">&quot;abcdef&quot;</span><span class="p">)</span>   <span class="c1"># Match</span>
<span class="go">&lt;_sre.SRE_Match object; span=(2, 3), match=&#39;c&#39;&gt;</span>
</pre></div>
</div>
<p>Regular expressions beginning with <code class="docutils literal notranslate"><span class="pre">'^'</span></code> can be used with <a class="reference internal" href="#re.search" title="re.search"><code class="xref py py-func docutils literal notranslate"><span class="pre">search()</span></code></a> to
restrict the match at the beginning of the string:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">&quot;c&quot;</span><span class="p">,</span> <span class="s2">&quot;abcdef&quot;</span><span class="p">)</span>    <span class="c1"># No match</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s2">&quot;^c&quot;</span><span class="p">,</span> <span class="s2">&quot;abcdef&quot;</span><span class="p">)</span>  <span class="c1"># No match</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s2">&quot;^a&quot;</span><span class="p">,</span> <span class="s2">&quot;abcdef&quot;</span><span class="p">)</span>  <span class="c1"># Match</span>
<span class="go">&lt;_sre.SRE_Match object; span=(0, 1), match=&#39;a&#39;&gt;</span>
</pre></div>
</div>
<p>Note however that in <a class="reference internal" href="#re.MULTILINE" title="re.MULTILINE"><code class="xref py py-const docutils literal notranslate"><span class="pre">MULTILINE</span></code></a> mode <a class="reference internal" href="#re.match" title="re.match"><code class="xref py py-func docutils literal notranslate"><span class="pre">match()</span></code></a> only matches at the
beginning of the string, whereas using <a class="reference internal" href="#re.search" title="re.search"><code class="xref py py-func docutils literal notranslate"><span class="pre">search()</span></code></a> with a regular expression
beginning with <code class="docutils literal notranslate"><span class="pre">'^'</span></code> will match at the beginning of each line.</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s1">&#39;X&#39;</span><span class="p">,</span> <span class="s1">&#39;A</span><span class="se">\n</span><span class="s1">B</span><span class="se">\n</span><span class="s1">X&#39;</span><span class="p">,</span> <span class="n">re</span><span class="o">.</span><span class="n">MULTILINE</span><span class="p">)</span>  <span class="c1"># No match</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">re</span><span class="o">.</span><span class="n">search</span><span class="p">(</span><span class="s1">&#39;^X&#39;</span><span class="p">,</span> <span class="s1">&#39;A</span><span class="se">\n</span><span class="s1">B</span><span class="se">\n</span><span class="s1">X&#39;</span><span class="p">,</span> <span class="n">re</span><span class="o">.</span><span class="n">MULTILINE</span><span class="p">)</span>  <span class="c1"># Match</span>
<span class="go">&lt;_sre.SRE_Match object; span=(4, 5), match=&#39;X&#39;&gt;</span>
</pre></div>
</div>
</div>
<div class="section" id="making-a-phonebook">
<h3>6.2.5.4. Making a Phonebook<a class="headerlink" href="#making-a-phonebook" title="永久链接至标题">¶</a></h3>
<p><a class="reference internal" href="#re.split" title="re.split"><code class="xref py py-func docutils literal notranslate"><span class="pre">split()</span></code></a> splits a string into a list delimited by the passed pattern.  The
method is invaluable for converting textual data into data structures that can be
easily read and modified by Python as demonstrated in the following example that
creates a phonebook.</p>
<p>First, here is the input.  Normally it may come from a file, here we are using
triple-quoted string syntax:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">text</span> <span class="o">=</span> <span class="s2">&quot;&quot;&quot;Ross McFluff: 834.345.1254 155 Elm Street</span>
<span class="gp">...</span><span class="s2"></span>
<span class="gp">... </span><span class="s2">Ronald Heathmore: 892.345.3428 436 Finley Avenue</span>
<span class="gp">... </span><span class="s2">Frank Burger: 925.541.7625 662 South Dogwood Way</span>
<span class="gp">...</span><span class="s2"></span>
<span class="gp">...</span><span class="s2"></span>
<span class="gp">... </span><span class="s2">Heather Albrecht: 548.326.4584 919 Park Place&quot;&quot;&quot;</span>
</pre></div>
</div>
<p>The entries are separated by one or more newlines. Now we convert the string
into a list with each nonempty line having its own entry:</p>
<div class="highlight-pycon notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">entries</span> <span class="o">=</span> <span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="s2">&quot;</span><span class="se">\n</span><span class="s2">+&quot;</span><span class="p">,</span> <span class="n">text</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">entries</span>
<span class="go">[&#39;Ross McFluff: 834.345.1254 155 Elm Street&#39;,</span>
<span class="go">&#39;Ronald Heathmore: 892.345.3428 436 Finley Avenue&#39;,</span>
<span class="go">&#39;Frank Burger: 925.541.7625 662 South Dogwood Way&#39;,</span>
<span class="go">&#39;Heather Albrecht: 548.326.4584 919 Park Place&#39;]</span>
</pre></div>
</div>
<p>Finally, split each entry into a list with first name, last name, telephone
number, and address.  We use the <code class="docutils literal notranslate"><span class="pre">maxsplit</span></code> parameter of <a class="reference internal" href="#re.split" title="re.split"><code class="xref py py-func docutils literal notranslate"><span class="pre">split()</span></code></a>
because the address has spaces, our splitting pattern, in it:</p>
<div class="highlight-pycon notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="p">[</span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="s2">&quot;:? &quot;</span><span class="p">,</span> <span class="n">entry</span><span class="p">,</span> <span class="mi">3</span><span class="p">)</span> <span class="k">for</span> <span class="n">entry</span> <span class="ow">in</span> <span class="n">entries</span><span class="p">]</span>
<span class="go">[[&#39;Ross&#39;, &#39;McFluff&#39;, &#39;834.345.1254&#39;, &#39;155 Elm Street&#39;],</span>
<span class="go">[&#39;Ronald&#39;, &#39;Heathmore&#39;, &#39;892.345.3428&#39;, &#39;436 Finley Avenue&#39;],</span>
<span class="go">[&#39;Frank&#39;, &#39;Burger&#39;, &#39;925.541.7625&#39;, &#39;662 South Dogwood Way&#39;],</span>
<span class="go">[&#39;Heather&#39;, &#39;Albrecht&#39;, &#39;548.326.4584&#39;, &#39;919 Park Place&#39;]]</span>
</pre></div>
</div>
<p>The <code class="docutils literal notranslate"><span class="pre">:?</span></code> pattern matches the colon after the last name, so that it does not
occur in the result list.  With a <code class="docutils literal notranslate"><span class="pre">maxsplit</span></code> of <code class="docutils literal notranslate"><span class="pre">4</span></code>, we could separate the
house number from the street name:</p>
<div class="highlight-pycon notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="p">[</span><span class="n">re</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="s2">&quot;:? &quot;</span><span class="p">,</span> <span class="n">entry</span><span class="p">,</span> <span class="mi">4</span><span class="p">)</span> <span class="k">for</span> <span class="n">entry</span> <span class="ow">in</span> <span class="n">entries</span><span class="p">]</span>
<span class="go">[[&#39;Ross&#39;, &#39;McFluff&#39;, &#39;834.345.1254&#39;, &#39;155&#39;, &#39;Elm Street&#39;],</span>
<span class="go">[&#39;Ronald&#39;, &#39;Heathmore&#39;, &#39;892.345.3428&#39;, &#39;436&#39;, &#39;Finley Avenue&#39;],</span>
<span class="go">[&#39;Frank&#39;, &#39;Burger&#39;, &#39;925.541.7625&#39;, &#39;662&#39;, &#39;South Dogwood Way&#39;],</span>
<span class="go">[&#39;Heather&#39;, &#39;Albrecht&#39;, &#39;548.326.4584&#39;, &#39;919&#39;, &#39;Park Place&#39;]]</span>
</pre></div>
</div>
</div>
<div class="section" id="text-munging">
<h3>6.2.5.5. Text Munging<a class="headerlink" href="#text-munging" title="永久链接至标题">¶</a></h3>
<p><a class="reference internal" href="#re.sub" title="re.sub"><code class="xref py py-func docutils literal notranslate"><span class="pre">sub()</span></code></a> replaces every occurrence of a pattern with a string or the
result of a function.  This example demonstrates using <a class="reference internal" href="#re.sub" title="re.sub"><code class="xref py py-func docutils literal notranslate"><span class="pre">sub()</span></code></a> with
a function to &quot;munge&quot; text, or randomize the order of all the characters
in each word of a sentence except for the first and last characters:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="k">def</span> <span class="nf">repl</span><span class="p">(</span><span class="n">m</span><span class="p">):</span>
<span class="gp">... </span>    <span class="n">inner_word</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">2</span><span class="p">))</span>
<span class="gp">... </span>    <span class="n">random</span><span class="o">.</span><span class="n">shuffle</span><span class="p">(</span><span class="n">inner_word</span><span class="p">)</span>
<span class="gp">... </span>    <span class="k">return</span> <span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="o">+</span> <span class="s2">&quot;&quot;</span><span class="o">.</span><span class="n">join</span><span class="p">(</span><span class="n">inner_word</span><span class="p">)</span> <span class="o">+</span> <span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">text</span> <span class="o">=</span> <span class="s2">&quot;Professor Abdolmalek, please report your absences promptly.&quot;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">re</span><span class="o">.</span><span class="n">sub</span><span class="p">(</span><span class="sa">r</span><span class="s2">&quot;(\w)(\w+)(\w)&quot;</span><span class="p">,</span> <span class="n">repl</span><span class="p">,</span> <span class="n">text</span><span class="p">)</span>
<span class="go">&#39;Poefsrosr Aealmlobdk, pslaee reorpt your abnseces plmrptoy.&#39;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">re</span><span class="o">.</span><span class="n">sub</span><span class="p">(</span><span class="sa">r</span><span class="s2">&quot;(\w)(\w+)(\w)&quot;</span><span class="p">,</span> <span class="n">repl</span><span class="p">,</span> <span class="n">text</span><span class="p">)</span>
<span class="go">&#39;Pofsroser Aodlambelk, plasee reoprt yuor asnebces potlmrpy.&#39;</span>
</pre></div>
</div>
</div>
<div class="section" id="finding-all-adverbs">
<h3>6.2.5.6. Finding all Adverbs<a class="headerlink" href="#finding-all-adverbs" title="永久链接至标题">¶</a></h3>
<p><a class="reference internal" href="#re.findall" title="re.findall"><code class="xref py py-func docutils literal notranslate"><span class="pre">findall()</span></code></a> matches <em>all</em> occurrences of a pattern, not just the first
one as <a class="reference internal" href="#re.search" title="re.search"><code class="xref py py-func docutils literal notranslate"><span class="pre">search()</span></code></a> does.  For example, if a writer wanted to
find all of the adverbs in some text, they might use <a class="reference internal" href="#re.findall" title="re.findall"><code class="xref py py-func docutils literal notranslate"><span class="pre">findall()</span></code></a> in
the following manner:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">text</span> <span class="o">=</span> <span class="s2">&quot;He was carefully disguised but captured quickly by police.&quot;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">re</span><span class="o">.</span><span class="n">findall</span><span class="p">(</span><span class="sa">r</span><span class="s2">&quot;\w+ly&quot;</span><span class="p">,</span> <span class="n">text</span><span class="p">)</span>
<span class="go">[&#39;carefully&#39;, &#39;quickly&#39;]</span>
</pre></div>
</div>
</div>
<div class="section" id="finding-all-adverbs-and-their-positions">
<h3>6.2.5.7. Finding all Adverbs and their Positions<a class="headerlink" href="#finding-all-adverbs-and-their-positions" title="永久链接至标题">¶</a></h3>
<p>If one wants more information about all matches of a pattern than the matched
text, <a class="reference internal" href="#re.finditer" title="re.finditer"><code class="xref py py-func docutils literal notranslate"><span class="pre">finditer()</span></code></a> is useful as it provides <a class="reference internal" href="#match-objects"><span class="std std-ref">match objects</span></a> instead of strings.  Continuing with the previous example, if
a writer wanted to find all of the adverbs <em>and their positions</em> in
some text, they would use <a class="reference internal" href="#re.finditer" title="re.finditer"><code class="xref py py-func docutils literal notranslate"><span class="pre">finditer()</span></code></a> in the following manner:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">text</span> <span class="o">=</span> <span class="s2">&quot;He was carefully disguised but captured quickly by police.&quot;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">for</span> <span class="n">m</span> <span class="ow">in</span> <span class="n">re</span><span class="o">.</span><span class="n">finditer</span><span class="p">(</span><span class="sa">r</span><span class="s2">&quot;\w+ly&quot;</span><span class="p">,</span> <span class="n">text</span><span class="p">):</span>
<span class="gp">... </span>    <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;</span><span class="si">%02d</span><span class="s1">-</span><span class="si">%02d</span><span class="s1">: </span><span class="si">%s</span><span class="s1">&#39;</span> <span class="o">%</span> <span class="p">(</span><span class="n">m</span><span class="o">.</span><span class="n">start</span><span class="p">(),</span> <span class="n">m</span><span class="o">.</span><span class="n">end</span><span class="p">(),</span> <span class="n">m</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="mi">0</span><span class="p">)))</span>
<span class="go">07-16: carefully</span>
<span class="go">40-47: quickly</span>
</pre></div>
</div>
</div>
<div class="section" id="raw-string-notation">
<h3>6.2.5.8. Raw String Notation<a class="headerlink" href="#raw-string-notation" title="永久链接至标题">¶</a></h3>
<p>Raw string notation (<code class="docutils literal notranslate"><span class="pre">r&quot;text&quot;</span></code>) keeps regular expressions sane.  Without it,
every backslash (<code class="docutils literal notranslate"><span class="pre">'\'</span></code>) in a regular expression would have to be prefixed with
another one to escape it.  For example, the two following lines of code are
functionally identical:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">&quot;\W(.)\1\W&quot;</span><span class="p">,</span> <span class="s2">&quot; ff &quot;</span><span class="p">)</span>
<span class="go">&lt;_sre.SRE_Match object; span=(0, 4), match=&#39; ff &#39;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">&quot;</span><span class="se">\\</span><span class="s2">W(.)</span><span class="se">\\</span><span class="s2">1</span><span class="se">\\</span><span class="s2">W&quot;</span><span class="p">,</span> <span class="s2">&quot; ff &quot;</span><span class="p">)</span>
<span class="go">&lt;_sre.SRE_Match object; span=(0, 4), match=&#39; ff &#39;&gt;</span>
</pre></div>
</div>
<p>When one wants to match a literal backslash, it must be escaped in the regular
expression.  With raw string notation, this means <code class="docutils literal notranslate"><span class="pre">r&quot;\\&quot;</span></code>.  Without raw string
notation, one must use <code class="docutils literal notranslate"><span class="pre">&quot;\\\\&quot;</span></code>, making the following lines of code
functionally identical:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="sa">r</span><span class="s2">&quot;</span><span class="se">\\</span><span class="s2">&quot;</span><span class="p">,</span> <span class="sa">r</span><span class="s2">&quot;</span><span class="se">\\</span><span class="s2">&quot;</span><span class="p">)</span>
<span class="go">&lt;_sre.SRE_Match object; span=(0, 1), match=&#39;\\&#39;&gt;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">re</span><span class="o">.</span><span class="n">match</span><span class="p">(</span><span class="s2">&quot;</span><span class="se">\\\\</span><span class="s2">&quot;</span><span class="p">,</span> <span class="sa">r</span><span class="s2">&quot;</span><span class="se">\\</span><span class="s2">&quot;</span><span class="p">)</span>
<span class="go">&lt;_sre.SRE_Match object; span=(0, 1), match=&#39;\\&#39;&gt;</span>
</pre></div>
</div>
</div>
<div class="section" id="writing-a-tokenizer">
<h3>6.2.5.9. Writing a Tokenizer<a class="headerlink" href="#writing-a-tokenizer" title="永久链接至标题">¶</a></h3>
<p>A <a class="reference external" href="https://en.wikipedia.org/wiki/Lexical_analysis">tokenizer or scanner</a>
analyzes a string to categorize groups of characters.  This is a useful first
step in writing a compiler or interpreter.</p>
<p>The text categories are specified with regular expressions.  The technique is
to combine those into a single master regular expression and to loop over
successive matches:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">collections</span>
<span class="kn">import</span> <span class="nn">re</span>

<span class="n">Token</span> <span class="o">=</span> <span class="n">collections</span><span class="o">.</span><span class="n">namedtuple</span><span class="p">(</span><span class="s1">&#39;Token&#39;</span><span class="p">,</span> <span class="p">[</span><span class="s1">&#39;typ&#39;</span><span class="p">,</span> <span class="s1">&#39;value&#39;</span><span class="p">,</span> <span class="s1">&#39;line&#39;</span><span class="p">,</span> <span class="s1">&#39;column&#39;</span><span class="p">])</span>

<span class="k">def</span> <span class="nf">tokenize</span><span class="p">(</span><span class="n">code</span><span class="p">):</span>
    <span class="n">keywords</span> <span class="o">=</span> <span class="p">{</span><span class="s1">&#39;IF&#39;</span><span class="p">,</span> <span class="s1">&#39;THEN&#39;</span><span class="p">,</span> <span class="s1">&#39;ENDIF&#39;</span><span class="p">,</span> <span class="s1">&#39;FOR&#39;</span><span class="p">,</span> <span class="s1">&#39;NEXT&#39;</span><span class="p">,</span> <span class="s1">&#39;GOSUB&#39;</span><span class="p">,</span> <span class="s1">&#39;RETURN&#39;</span><span class="p">}</span>
    <span class="n">token_specification</span> <span class="o">=</span> <span class="p">[</span>
        <span class="p">(</span><span class="s1">&#39;NUMBER&#39;</span><span class="p">,</span>  <span class="sa">r</span><span class="s1">&#39;\d+(\.\d*)?&#39;</span><span class="p">),</span>  <span class="c1"># Integer or decimal number</span>
        <span class="p">(</span><span class="s1">&#39;ASSIGN&#39;</span><span class="p">,</span>  <span class="sa">r</span><span class="s1">&#39;:=&#39;</span><span class="p">),</span>           <span class="c1"># Assignment operator</span>
        <span class="p">(</span><span class="s1">&#39;END&#39;</span><span class="p">,</span>     <span class="sa">r</span><span class="s1">&#39;;&#39;</span><span class="p">),</span>            <span class="c1"># Statement terminator</span>
        <span class="p">(</span><span class="s1">&#39;ID&#39;</span><span class="p">,</span>      <span class="sa">r</span><span class="s1">&#39;[A-Za-z]+&#39;</span><span class="p">),</span>    <span class="c1"># Identifiers</span>
        <span class="p">(</span><span class="s1">&#39;OP&#39;</span><span class="p">,</span>      <span class="sa">r</span><span class="s1">&#39;[+\-*/]&#39;</span><span class="p">),</span>      <span class="c1"># Arithmetic operators</span>
        <span class="p">(</span><span class="s1">&#39;NEWLINE&#39;</span><span class="p">,</span> <span class="sa">r</span><span class="s1">&#39;\n&#39;</span><span class="p">),</span>           <span class="c1"># Line endings</span>
        <span class="p">(</span><span class="s1">&#39;SKIP&#39;</span><span class="p">,</span>    <span class="sa">r</span><span class="s1">&#39;[ \t]+&#39;</span><span class="p">),</span>       <span class="c1"># Skip over spaces and tabs</span>
        <span class="p">(</span><span class="s1">&#39;MISMATCH&#39;</span><span class="p">,</span><span class="sa">r</span><span class="s1">&#39;.&#39;</span><span class="p">),</span>            <span class="c1"># Any other character</span>
    <span class="p">]</span>
    <span class="n">tok_regex</span> <span class="o">=</span> <span class="s1">&#39;|&#39;</span><span class="o">.</span><span class="n">join</span><span class="p">(</span><span class="s1">&#39;(?P&lt;</span><span class="si">%s</span><span class="s1">&gt;</span><span class="si">%s</span><span class="s1">)&#39;</span> <span class="o">%</span> <span class="n">pair</span> <span class="k">for</span> <span class="n">pair</span> <span class="ow">in</span> <span class="n">token_specification</span><span class="p">)</span>
    <span class="n">line_num</span> <span class="o">=</span> <span class="mi">1</span>
    <span class="n">line_start</span> <span class="o">=</span> <span class="mi">0</span>
    <span class="k">for</span> <span class="n">mo</span> <span class="ow">in</span> <span class="n">re</span><span class="o">.</span><span class="n">finditer</span><span class="p">(</span><span class="n">tok_regex</span><span class="p">,</span> <span class="n">code</span><span class="p">):</span>
        <span class="n">kind</span> <span class="o">=</span> <span class="n">mo</span><span class="o">.</span><span class="n">lastgroup</span>
        <span class="n">value</span> <span class="o">=</span> <span class="n">mo</span><span class="o">.</span><span class="n">group</span><span class="p">(</span><span class="n">kind</span><span class="p">)</span>
        <span class="k">if</span> <span class="n">kind</span> <span class="o">==</span> <span class="s1">&#39;NEWLINE&#39;</span><span class="p">:</span>
            <span class="n">line_start</span> <span class="o">=</span> <span class="n">mo</span><span class="o">.</span><span class="n">end</span><span class="p">()</span>
            <span class="n">line_num</span> <span class="o">+=</span> <span class="mi">1</span>
        <span class="k">elif</span> <span class="n">kind</span> <span class="o">==</span> <span class="s1">&#39;SKIP&#39;</span><span class="p">:</span>
            <span class="k">pass</span>
        <span class="k">elif</span> <span class="n">kind</span> <span class="o">==</span> <span class="s1">&#39;MISMATCH&#39;</span><span class="p">:</span>
            <span class="k">raise</span> <span class="ne">RuntimeError</span><span class="p">(</span><span class="n">f</span><span class="s1">&#39;</span><span class="si">{value!r}</span><span class="s1"> unexpected on line </span><span class="si">{line_num}</span><span class="s1">&#39;</span><span class="p">)</span>
        <span class="k">else</span><span class="p">:</span>
            <span class="k">if</span> <span class="n">kind</span> <span class="o">==</span> <span class="s1">&#39;ID&#39;</span> <span class="ow">and</span> <span class="n">value</span> <span class="ow">in</span> <span class="n">keywords</span><span class="p">:</span>
                <span class="n">kind</span> <span class="o">=</span> <span class="n">value</span>
            <span class="n">column</span> <span class="o">=</span> <span class="n">mo</span><span class="o">.</span><span class="n">start</span><span class="p">()</span> <span class="o">-</span> <span class="n">line_start</span>
            <span class="k">yield</span> <span class="n">Token</span><span class="p">(</span><span class="n">kind</span><span class="p">,</span> <span class="n">value</span><span class="p">,</span> <span class="n">line_num</span><span class="p">,</span> <span class="n">column</span><span class="p">)</span>

<span class="n">statements</span> <span class="o">=</span> <span class="s1">&#39;&#39;&#39;</span>
<span class="s1">    IF quantity THEN</span>
<span class="s1">        total := total + price * quantity;</span>
<span class="s1">        tax := price * 0.05;</span>
<span class="s1">    ENDIF;</span>
<span class="s1">&#39;&#39;&#39;</span>

<span class="k">for</span> <span class="n">token</span> <span class="ow">in</span> <span class="n">tokenize</span><span class="p">(</span><span class="n">statements</span><span class="p">):</span>
    <span class="nb">print</span><span class="p">(</span><span class="n">token</span><span class="p">)</span>
</pre></div>
</div>
<p>The tokenizer produces the following output:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">Token</span><span class="p">(</span><span class="n">typ</span><span class="o">=</span><span class="s1">&#39;IF&#39;</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">&#39;IF&#39;</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">2</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">4</span><span class="p">)</span>
<span class="n">Token</span><span class="p">(</span><span class="n">typ</span><span class="o">=</span><span class="s1">&#39;ID&#39;</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">&#39;quantity&#39;</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">2</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">7</span><span class="p">)</span>
<span class="n">Token</span><span class="p">(</span><span class="n">typ</span><span class="o">=</span><span class="s1">&#39;THEN&#39;</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">&#39;THEN&#39;</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">2</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">16</span><span class="p">)</span>
<span class="n">Token</span><span class="p">(</span><span class="n">typ</span><span class="o">=</span><span class="s1">&#39;ID&#39;</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">&#39;total&#39;</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">3</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">8</span><span class="p">)</span>
<span class="n">Token</span><span class="p">(</span><span class="n">typ</span><span class="o">=</span><span class="s1">&#39;ASSIGN&#39;</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">&#39;:=&#39;</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">3</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">14</span><span class="p">)</span>
<span class="n">Token</span><span class="p">(</span><span class="n">typ</span><span class="o">=</span><span class="s1">&#39;ID&#39;</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">&#39;total&#39;</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">3</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">17</span><span class="p">)</span>
<span class="n">Token</span><span class="p">(</span><span class="n">typ</span><span class="o">=</span><span class="s1">&#39;OP&#39;</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">&#39;+&#39;</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">3</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">23</span><span class="p">)</span>
<span class="n">Token</span><span class="p">(</span><span class="n">typ</span><span class="o">=</span><span class="s1">&#39;ID&#39;</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">&#39;price&#39;</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">3</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">25</span><span class="p">)</span>
<span class="n">Token</span><span class="p">(</span><span class="n">typ</span><span class="o">=</span><span class="s1">&#39;OP&#39;</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">&#39;*&#39;</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">3</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">31</span><span class="p">)</span>
<span class="n">Token</span><span class="p">(</span><span class="n">typ</span><span class="o">=</span><span class="s1">&#39;ID&#39;</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">&#39;quantity&#39;</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">3</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">33</span><span class="p">)</span>
<span class="n">Token</span><span class="p">(</span><span class="n">typ</span><span class="o">=</span><span class="s1">&#39;END&#39;</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">&#39;;&#39;</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">3</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">41</span><span class="p">)</span>
<span class="n">Token</span><span class="p">(</span><span class="n">typ</span><span class="o">=</span><span class="s1">&#39;ID&#39;</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">&#39;tax&#39;</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">4</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">8</span><span class="p">)</span>
<span class="n">Token</span><span class="p">(</span><span class="n">typ</span><span class="o">=</span><span class="s1">&#39;ASSIGN&#39;</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">&#39;:=&#39;</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">4</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">12</span><span class="p">)</span>
<span class="n">Token</span><span class="p">(</span><span class="n">typ</span><span class="o">=</span><span class="s1">&#39;ID&#39;</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">&#39;price&#39;</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">4</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">15</span><span class="p">)</span>
<span class="n">Token</span><span class="p">(</span><span class="n">typ</span><span class="o">=</span><span class="s1">&#39;OP&#39;</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">&#39;*&#39;</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">4</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">21</span><span class="p">)</span>
<span class="n">Token</span><span class="p">(</span><span class="n">typ</span><span class="o">=</span><span class="s1">&#39;NUMBER&#39;</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">&#39;0.05&#39;</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">4</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">23</span><span class="p">)</span>
<span class="n">Token</span><span class="p">(</span><span class="n">typ</span><span class="o">=</span><span class="s1">&#39;END&#39;</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">&#39;;&#39;</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">4</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">27</span><span class="p">)</span>
<span class="n">Token</span><span class="p">(</span><span class="n">typ</span><span class="o">=</span><span class="s1">&#39;ENDIF&#39;</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">&#39;ENDIF&#39;</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">5</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">4</span><span class="p">)</span>
<span class="n">Token</span><span class="p">(</span><span class="n">typ</span><span class="o">=</span><span class="s1">&#39;END&#39;</span><span class="p">,</span> <span class="n">value</span><span class="o">=</span><span class="s1">&#39;;&#39;</span><span class="p">,</span> <span class="n">line</span><span class="o">=</span><span class="mi">5</span><span class="p">,</span> <span class="n">column</span><span class="o">=</span><span class="mi">9</span><span class="p">)</span>
</pre></div>
</div>
<table class="docutils citation" frame="void" id="frie09" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label"><a class="fn-backref" href="#id1">[Frie09]</a></td><td>Friedl, Jeffrey. Mastering Regular Expressions. 3rd ed., O'Reilly
Media, 2009. The third edition of the book no longer covers Python at all,
but the first edition covered writing good regular expression patterns in
great detail.</td></tr>
</tbody>
</table>
</div>
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<li><a class="reference internal" href="#regular-expression-syntax">6.2.1. Regular Expression Syntax</a></li>
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